1. Heat oven to 350°F. Line 36 small muffin cups (1-3/4 inches in diameter) with paper or foil bake cups. Remove wrappers from peanut butter cups. Coarsely chop 24 peanut butter cups; set aside.
2. Beat butter and peanut butter until well blended. Add brown sugar, granulated sugar, egg, milk and vanilla; beat thoroughly. Stir together flour, baking soda and salt; add to butter mixture, beating until well blended. Stir in chopped peanut butter cups.
3. Roll dough into 36 equal balls (about 1-1/4 inches); place in prepared pans. Bake 12 to 14 minutes or until set. Remove from oven; cool completely in pans on wire rack.
4. Cut remaining peanut butter cups into quarters; set aside. Prepare COCOA DRIZZLE GLAZE; drizzle over cookie tops. Immediately garnish with decorative candies, if desired. Before drizzle sets, top each cookie with peanut butter quarter. Makes 36 cookie cups.
COCOA DRIZZLE GLAZE: Place 1 tablespoon butter or margarine in small microwave-safe bowl. Microwave at MEDIUM (50%) 20 to 30 seconds or until melted. Stir in 1 tablespoon HERSHEY'S Cocoa and 1 tablespoon water. Microwave at MEDIUM 15 to 30 seconds or just until mixture is hot, slightly thickened and smooth when stirred. Do not boil. Gradually add 1/2 cup powdered sugar and 1/2 teaspoon vanilla extract, beating with whisk until smooth. If necessary, add additional water, a few drops at a time, until of desired consistency. About 1/4 cup glaze.