1½ cups plus 2 tbsp. all-purpose flour
6 tbsp. Dutch-process cocoa
½ tsp. baking soda
½ tsp. coarse salt
¾ stick (6 tbsp.) unsalted butter, at room temperature
¼ cup plus 2 tbsp. creamy peanut butter
½ cup sugar
½ cup brown sugar
1 large egg
1 tsp. vanilla extract
2 tbsp. milk
2 cups coarsely chopped peanut butter cups, divided*