Blend sugar, butter, vanilla and egg yolks. Lightly spoon in flour and baking powder. Make into balls. Put cupcake liners into cupcake tins. Put the balls into the cupcake liners. Put Reese's peanut butter cups into center of cookie and press down lightly. Bake at 350 for 12 minutes. Remove and place cookies on cooling rack. (If you want to make a double batch, of course double the recipe, and purchase a 22 oz. bag of Reese's miniatures).