Preheat oven to 350°F. Spray 13 in. x 9 in. pan with vegetable pan spray.

In medium bowl, stir together flour, cocoa powder, baking powder, baking soda and salt.

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.

Bake 28-30 minutes or until toothpick inserted in center comes out almost clean. Remove to cooling grid; cool completely.