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Spooky Black Widow Peanut Butter Bars. Doughy buttery, peanut butter cookie base, layered with creamy peanut butter, and the most delectable, roll your eyes back good, chocolate frosting that’s rich and fudgy. They’re sweet, salty, heavy on the peanut butter, extra chocolatey, and totally decked out for Halloween. The perfect spooky treat to enjoy all October long.

Black Widow Peanut Butter Bars |

It’s spooky season! I know it’s a little dorky, but I’m so excited for the Halloween season this year. I’m having so much fun creating Halloween themed desserts and drinks for the month.

I figured these would be the perfect spooky bars to kick off the month of all things spooky. Their so easy to make, delicious, and in my opinion, so cute too!

I love the little spider web and black spiders all around.

Black Widow Peanut Butter Bars |

The details

I tried to keep these as simple as possible, using my favorite peanut butter bars as a base and sweet chocolate icing.

Start with the peanut cookie base. These don’t even require a mixer, just mix with a spoon and bake. So simple. As soon as the peanut bars come out of the oven, dollop them with a hefty amount of creamy peanut butter. The key is to add the peanut butter while the bars are still warm. The heat from the bars allows the peanut butter to melt into one even layer and makes spreading the peanut butter out very simple.

Now let the bars chill completely.

Black Widow Peanut Butter Bars |

(spiders body with melted chocolate)

Black Widow Peanut Butter Bars |

(spiders after adding the eyes and legs)

Black Widow Peanut Butter Bars |

In the meantime, make the frosting.

The frosting needs to be thick and fudgy, but yet soft and almost runny. Think of a just set top that has glazed over and stiffened, but then underneath is fudgy, loose frosting.

The mix of ingredients is basic…butter, sugar, cocoa powder, vanilla, and milk.

Black Widow Peanut Butter Bars |

Now the decorating, start with the web

For the web, I used melted marshmallows and stretched the marshmallows over the set bars. It’s the easiest thing, and honestly, really fun. If you have kids, this is a fun task for them to do.

For the spiders, I used chocolate whoppers, a little melted chocolate, and some sprinkles. Now, here’s what I will say about the spiders, if you want to use small plastic spiders, go for it! Those will be really cute and people will easily be able to pick them off if they choose.

Black Widow Peanut Butter Bars |

If you want to make them homemade, that’s great too, it’s just going to take a little more time. I advise you to really use the photos for guidance, but I did my best to explain the process.

Two whopper balls for the spider’s back, melted chocolate for the legs, and then a couple of candy eyes.

Black Widow Peanut Butter Bars |

And that’s it! Aside from the spiders, really simple, and so fun to make! These bars are so great to enjoy all month long. Take them to your next Halloween party, and then of course…serve them up on Halloween night!

See you all tomorrow for our first Halloween cocktail of the season!

Black Widow Peanut Butter Bars |

Looking for other fall soup recipes? Here are a few ideas: 

Hocus Pocus Spellbook Brownies

Spooky Halloween Pretzels

BOO! Chocolate Peanut Butter Bars

Lastly, if you make these Black Widow Peanut Butter Bars be sure to leave a comment and/or give this recipe a rating! Above all, I love to hear from you guys and always do my best to respond to each and every comment. And of course, if you do make this recipe, don’t forget to tag me on Instagram! Looking through the photos of recipes you all have made is my favorite!

Black Widow Peanut Butter Bars

Prep Time 50 minutes
Cook Time 20 minutes
Total Time 1 hour 10 minutes
Servings: 24 bars
Calories Per Serving: 310 kcal

Nutritional information is only an estimate. The accuracy of the nutritional information for any recipe on this site is not guaranteed.


Peanut Butter Bars


For decorating


  • 1. Preheat the oven to 350° F. Line a 9×13 inch baking dish with parchment paper.
    2. In a microwave safe bowl, melt together the butter and 1/2 cup peanut butter, stirring every 30 seconds until melted. Stir in the brown sugar, sugar, eggs, and vanilla. Add the flour, baking powder, and salt.
    3. Press/spread the dough out into the prepared dish. Transfer to the oven and bake for 18-22 minutes, until just set in the center. Remove from the oven and dollop tablespoon size spoonfuls of the peanut butter over the bars. Lightly spread the peanut butter in an even layer. Let cool completely.
    4. To make the frosting. Add the butter, 2 cups powdered sugar, cocoa powder, vanilla, and 1/4 cup warm milk to the bowl of a stand mixer. Beat until smooth, adding additional warm milk until the frosting becomes thicker but still drizzly. Taste, adding more sugar if needed. Spread the frosting over the bars. Let set for 1-ish hour.
    5. To make the web, melt the marshmallows in the microwave on 30 second intervals, stirring after each, until melted and smooth. Let cool 3-5 minutes and then use your hands to stretch/pull the melted marshmallow over the bars to create a spider web. Go in as many directions as possible. It will be messy, but fun!
    6. To make the spiders, line a baking sheet with parchment paper. Spoon the chocolate into a piping bag with a fine tip or ziplock bag with the corner snipped off. Pipe two small, 1/3 inch dots of chocolate onto the paper side by side. Place 1 whopper on each dot, then draw 2-3 legs on either side of the whoppers for the legs. Sprinkle the legs with sprinkles. Place two tiny dots on either side of 1 whopper for the eyes. Place the tray in the freezer for 15 minutes to harden, then gently peel away the spiders and place them on top of the bars. Slice and enjoy!
    7. Store the bars in a cool dry place, either in the fridge or at room temp.
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Black Widow Peanut Butter Bars |

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  1. This is a great recipe and is easier than it looks! We sprayed some cooking spray on the bowl for melting the marshmallows and our hands for stretching the marshmallow and this really helped with the stickiness. It was very fun to make and yummy too!

    1. Hey Shelby,
      Happy Sunday! I am delighted to hear that this recipe was enjoyed, thanks so much for making it! xTieghan

  2. Delicious! Even my friend who doesn’t like peanut butter and chocolate combinations loved them! I did not have any issue getting the marshmallows to stick. Though, my frosting never got “hard”. I followed the directions and left the frosting just as she describes and the frosting remained soft after set. So, the marshmallows stuck great. Maybe people let their frosting get too thick and thus too hard? The spiders were super easy to make and such a fun addition. Defiantly making these again!

  3. 5 stars
    So good and fun to decorate! I baked them on the shorter side of the suggested baking time which was perfect. I recommend making the frosting just a little more dense so it sets better and definitely refrigerate / freeze before cutting the bars. I used chocolate covered peanuts instead of whoppers for the spiders which complimented the rest of the ingredients well. I struggled getting the melted marshmallows to stick to the bars rather than just my fingers, so if you have any tips for next time that would be appreciated!

  4. 5 stars
    Made for Halloween party, turned out great. Don’t like marshmallows so I used melted white chocolate for web, candy eyes & spiders.

  5. Hi there! Planning on making this tomorrow for Halloween ? I only ever have unsalted butter in my fridge. Can I still use that and throw in a pinch of salt? ?

  6. Hello! Sorry if I missed the quantity but….how many/much marshmallows do you melt? Everything’s ready to assemble but just curious on a correct amount of marshmallows. Thanks!

  7. Hi! Made these today with my friend and they turned out great and were really fun to make! We used milk duds as the spiders head (we like the taste more than whoppers) and we cut a Lindon dark chocolate in half for the body which gave it a fun size discrepancy and made the spiders look kind of tarantula like. Some tips from us:
    -err on the shorter side of the 18-22 min baking time to keep the bars from getting dry
    -let the frosting cool and harden before putting the Marshmellow web on
    -make the spider legs a bit thicker than you think and pull all spiders off the wax paper quickly once removing from the freezer for best results
    -freeze the whole dish for 5-10 min before cutting as it will help everything stay together better

    1. Hey! This is awesome, I’m so happy to hear this recipe turned out the way you’d hoped! And thanks for sharing all your tips and tricks! 🙂 xTieghan

  8. You think I can cut out a bit of the sugar from the bars? Maybe only the brown sugar? That seems like way too much sugar :O

    1. Hi there! Yes, you can cut out some sugar from this recipe, you could sub honey or maple syrup to keep the sweetness! xTieghan

  9. 5 stars
    OK made these a second time as a double batch. This time my butter was fully room temperature and there was definitely a change in consistency for the icing. My kids were distracting me and I ended up cooking the base a bit too long. Definitely better when it’s not so crisp. I didn’t measure my peanut butter but I used a whole costco size tub and I should have used more. I also used less powdered sugar (even though I tasted it and thought it was OK…) more is better.
    I attempted the webs one more time and it was still an awful mess. I shopped for more eyes at the grocery store and they were all sold out so with the silver sprinkles they looked more like tarantulas.
    So for next time:
    -Cool butter
    – More peanut butter
    -More powdered sugar
    – White chocolate web
    Thanks again! Like I said before everyone loved them so I had to double up this time. I’m sure I’lll have to make it again before the month is up.

    1. 5 stars
      I was so excited to try this recipe! The cookie and icing turned out amazing! We had the same problem with the webs as some of the other reviewers. The marshmallow wouldn’t stick to the cookie. We tried with 2 different batches of marshmallows. The first we let sit for 5 minutes after heating. That didn’t work. So the second attempt, we worked with the marshmallow almost right out of the microwave and that seemed to work a little better. I felt like Clark Griswald when he got sap all over him! I my hands were sticking to everything but the cookie. Maybe my icing was too loose! Anyway, it didn’t matter because the bars turned out delicious! We didn’t get a chance to make the spiders as my kids wanted to dive right in! My kids said it was the best thing I’ve made in a while! Can’t wait to make another batch!!! Thanks for the recipe and I love the creativity ❤️

      1. Hi there! Thanks so much for making this recipe, I hope you enjoyed it! Sorry about the marshmallow mess but it sounds like it turned out delish! Happy Weekend 🙂 xTieghan

  10. So excited to make these for a Halloween party! How far in advance could they be made and still look like I made them the same day? Trying to squeeze some baking in with a newborn!

      1. I have the same question as Adrienne,
        do we use 1/2 cup of peanut butter in the cake and the remaining 1 1/2 cups for the spread on top of the cake? And if so, why is it necessary to dollop tablespoon size spoonfuls of peanut butter onto the cake, when I can just spread the remaining
        1 1/2 cups of peanut butter on the cake?