Follow the recipe directions to prepare the sugar cookie dough.
Roll balls of dough that will fill the (sprayed with cooking spray) miniature muffin tin cavities 3/4ths the way full. Press into the muffin tin and slightly indent the center and press the dough up the sides.
Bake for 8-10 minutes or until the tops are lightly browned.
Remove and press the centers down deeply with a teaspoon measuring spoon. Allow to cool for 1-2 minutes and then gently twist the top until the cookie comes out. (Check out the post for more tips on how to successfully remove the sugar cookie cups).
While the cookies are cooking, beat the heavy whipping cream and 1 tablespoon powdered sugar until soft peaks form and then set aside.
In another bowl, beat together the white chocolate peanut butter, cream cheese, milk, and vanilla extract.
Beat in the powdered sugar until smooth and creamy.
Using a spatula, fold in the whipped cream gently.
Transfer the mixture into a frosting bag that has been fitted with a star tip.
Pipe the mousse into the sugar cookie cups.
If desired, garnish with chocolate shavings. Make the chocolate shavings by using a vegetable peeler to "peel" the chocolate bar.