PREHEAT oven to 375° F.
COMBINE flour, cocoa, baking soda and salt in large bowl.
BEAT granulated sugar, brown sugar, butter and vanilla extract in large mixer bowl until combined. Beat in eggs. Gradually beat in flour mixture. Stir in Nestlé Hearts. Press into 9-inch-square baking pan.
BAKE for 18 to 20 minutes or until wooden pick inserted near center comes out clean. Cool in pan on wire rack. Cut into bars. Dust with powdered sugar before serving.