Cookie Base
Brownie
Make the cookie dough. Cream the softened butter and dark brown sugar until well combined. Add the egg and vanilla and mix until incorporated, scraping down the bowl as needed.
In a separate bowl, combine the flour, baking soda, baking powder, and salt. Add the dry ingredients to the butter mixture and mix just until a dough forms. Fold in the dark and milk chocolate chips.
Place eight 4-inch ring molds onto a parchment-lined sheet pan. Using a 2-ounce scoop, portion one scoop of cookie dough into each ring.
Press the cookie dough evenly across the bottom of each ring, then work some of the dough slightly up the sides to create a shallow cookie-dough shell. Freeze for about 30 minutes while preparing the brownie batter.
Make the brownie batter. Melt the 3 oz butter and ¼ cup dark chocolate chips together until smooth.
Sift together the flour, cocoa powder, and salt in a separate bowl.
Add the granulated sugar to the melted butter and chocolate and mix well. Add the eggs and vanilla and mix until thoroughly combined.
Add the sifted dry ingredients and mix just until incorporated. Fold in the ½ cup dark chocolate chips and ½ cup milk chocolate chips.
Remove the frozen cookie shells from the freezer. Using the same 2-ounce scoop, place one scoop of brownie batter into the center of each cookie shell.
Lightly coat your fingertips with cooking spray and gently press/spread the brownie batter into an even layer inside the cookie shell.
Bake at 325°F for about 30 minutes, until the cookie crust is golden brown and the brownie is set around the edges but remains soft and fudgy in the center.
Allow the brownie cookie pies to cool thoroughly before removing the rings and cutting. The brownie centers will continue to set considerably as they cool.