This seriously delicious twist on a brookie includes a Tagalong center that becomes warm and melted when baked. Serve these cookies fresh from the oven for the best taste.
Preheat the oven to 350 degrees F.
Spray a 12-cup muffin pan generously with nonstick cooking spray.
Combine the butter, peanut butter, and brown sugar in a mixing bowl. Beat to combine. Add in the egg, and beat to incorporate. Add the flour, baking soda, and baking powder. Beat to incorporate. Divide the cookie batter evenly among the 12 muffin cups. Place a Tagalong cookie on top of each cookie dough layer.
Melt the butter and chocolate chips over a double-boiler, stir in sugar. Once melted, transfer the chocolate to a mixing bowl. Add the eggs and vanilla extract, and stir to combine. Whisk together the flour, cocoa powder, salt, and baking powder. Stir the flour mixture into the chocolate batter. Top off each muffin tin with the brownie batter, being sure to fill in any gaps around the cookie.
Bake for 25 to 30 minutes. Let cool for about 45 minutes before serving.