Spray mini muffin cups with non stick cooking spray; set aside. Preheat oven to 350 degrees.

Beat butter, sugar, and brown sugar in a mixing bowl till creamy. Beat in egg and vanilla.

In a small bowl, whisk together (or sift) flour, cocoa, baking soda, baking powder, and salt. Stir into wet ingredients just till all flour is moistened.

Roll dough into 36 balls and place in prepared muffin pans.

Bake at 350° for 9-10 minutes.

While cookie cups are still hot, use the back of a round measuring spoon to make an indentation in each cup.

Let cool for 5-10 minutes in pans, then remove to cooling racks to cool completely.

After cookie cups are cool, prepare filling. Beat the cream with a hand mixer till stiff peaks form. Set aside.

In another bowl, beat together the peanut butter and powdered sugar till smooth. Gradually fold in the whipped cream.

Pipe peanut butter mousse into cookie cups and top each with half of a peanut butter cup.

Serve immediately, or chill for up to an hour.