In large bowl, beat butter and sugar with electric mixer until light and fluffy. Melt Dark Cocoa candy following package instructions. Stir into butter and sugar mixture. Add eggs, one at a time, beating well after each addition. Add vanilla. Add flour mixture and mix until just combined. Stir in ½ cup chopped walnuts. Press mixture evenly into prepared pan. Sprinkle remaining walnuts and sprinkles, over top.