Cream sugars, butter and Variegate with electric mixer fitted with paddle attachment until smooth. Add eggs, 1 at a time, mixing well after each. Beat in vanilla. Gradually add combined flour, cocoa, baking soda and salt in 3 additions, mixing until blended after each.
Spread dough evenly in parchment paper-lined half sheet pan coated with cooking spray. Sprinkle evenly with graham pieces and half the cookie pieces. Press down gently. Refrigerate 30 min.
Bake in 350°F standard oven 12 to 15 min. or until dough is firm to the touch. Cool in pan to room temperature. Sprinkle with remaining cookie pieces and marshmallows.
Bake 3 to 5 min. or until marshmallows are golden brown. Cool completely before cutting.