Start by making the hot fudge sauce. Stir together cocoa powder, brown sugar, corn syrup, cream, salt and half of the chopped milk chocolate. Place in a small sauce pan and cook over medium heat, stirring, until chocolate is melted. Cook mixture at a low boil, stirring occasionally for 5 minutes. Remove pan from heat, add remaining chocolate, butter and vanilla and stir until smooth. Place half the fudge sauce in a bowl and place in the freezer for 20 minutes. The rest of the sauce is not needed for the cookies. Keep in the fridge for whenever you want some homemade hot fudge sauce. Just re-heat in the microwave. Line a baking sheet with a silpat, parchment or wax paper.
After 20 minutes remove the sauce from the freezer and use a spoon to scoop out 1 to 2 teaspoons of fudge sauce. Use your finger and scrap the sauce off the spoon and onto the lined baking sheet. Repeat until there is no more sauce left. Don't worry about some "chips" being bigger and some smaller, mine were all different sizes and it worked great every time. When the pan is filled with the fudge "chips" place it the freezer for a least an hour or until you are ready to bake the cookies.
When ready to bake the cookies preheat the oven to 350 degrees F.
Line two baking sheets with parchment paper or silpats. Combine the flour, baking soda and salt in small bowl. Beat the butter, granulated sugar, brown sugar and vanilla extract in large mixer bowl until creamy. Add the eggs, beating well. Add in the frozen ice cream and beat until mostly combined. Gradually beat in the flour mixture. Stir in the sprinkles.
Scoop out about 1/4 cup of the dough and roll into a ball and place on the prepared baking sheet. Repeat with the remaining dough. When all the dough is rolled into balls remove a few of the fudge "chips" from the freezer at a time (keep the rest in the freezer at all times). You have to work quick here, or the fudge chips will start to soften. Next stuff each dough ball with 1 or 2 fudge chips making sure to cover the chips completely with dough and if you want stuff in 1 or 2 more fudge chips around the top of the dough ball so the are peeking out just a bit.
Bake for 18 to 20 minutes or until they have reached your desired doneness. I personally think that it is best to take the cookies out right between 17 and 18 minutes, but mine were very underdone.
Allow to cool five minutes and serve. Or, allow to cool completely and store in a single layer on a covered baking sheet.