3/4 c. (1 1/2 sticks) unsalted butter, at room temperature
1 (8-ounce) package cream cheese, at room temperature
1 lb. confectioners sugar
Red gel food coloring
3 chocolate wafer cookies (such as Nabisco Famous Chocolate Wafers)
Cornstarch, for work surface
Gold food coloring spray
Make the cake: Prepare cake mix and bake in a 9- by 13-inch pan according to the package directions. Once cool, transfer to a serving platter.
Make the frosting and decorate: Beat butter and cream cheese on low speed with an electric mixer until smooth, 1 to 2 minutes. Increase mixer speed to medium and gradually beat in confectioners sugar until light and fluffy, 1 to 2 minutes.
Transfer 1 cup frosting to a piping bag fitted with a large flat tip. Tint remaining frosting red and use to frost sides and top of cake. Refrigerate cake until no longer tacky, 5 to 10 minutes.
Pipe a 3-inch-wide strip, lengthwise, down the center of the cake with white frosting. Place 2 wafer cookies on top half and 1 on bottom for buttons.
Lightly dust a work surface with cornstarch and roll out white fondant. Cut into a 3-inch square. Using a small square cookie cutter or paring knife, cut out center to make a belt buckle. Transfer to a sheet of parchment paper and spray with gold spray; let dry, 8 to 10 minutes.
Roll black fondant into a 9- by 3-inch rectangle and place on cake between buttons. Top with belt buckle.