Preheat the oven to 350 degrees F. Grease one 10-12 inch skillet OR 4-6 smaller skillets.
Combine the flour, baking soda and salt (if using) in a small bowl.
Beat the butter, granulated sugar, brown sugar, vanilla and miso in large mixer bowl until creamy, about 3 to 5 minutes. Add the eggs and beat well until combined. Gradually beat in the flour mixture. Stir in the chocolate chips and pretzels.
In a small bowl, mix together the peanut butter, 1 teaspoon vanilla and a pinch of salt.
Spread half the cookie dough into your prepared skillet or skillets. Dollop the peanut butter onto the cookie dough in rounder teaspoons. Now place the remaining cookie dough gently over the peanut butter. Place the skillet or skillets on a cookie sheet.
Bake on the middle rack in the oven for 20-25 minutes for a large skillet, and 12-15 minutes for smaller skillets. It's very important to not over bake the skillet cookie, these are best eaten when the center is a little underdone. Remove from the oven and let cool 3-5 minutes...then DIG in. No plates required, just grab some spoons. If you like, add a scoop of ice cream, and/or a sprinkle of flaky sea salt. YUM.