1 18 1/4 ounce box yellow cake mix, plus ingredients listed on box
5 round (about 3 inches diameter) cookies with scalloped edges
2 16 ounce cans vanilla ready-to-spread frosting
Green sugar crystals
Pink sugar crystals
Yellow sugar crystals
Orange sugar crystals
5 ice cream cones
1 quart vanilla ice cream
Yellow liquid food coloring
1 4 1/4 ounce tube orange decorating icing, fitted with a star tip
1 4 1/4 ounce tube blue decorating icing, fitted with a writing tip
1. Heat oven to 350 degrees F. Prepare batter, bake, and cool cake layers according to package directions for two 9-inch round pans.
2. Spread cookies with a layer of frosting, then press into green sugar crystals. Place in a 9 x 13-inch baking pan; set aside. Spread a thin layer of frosting on ice-cream cones. Roll each cone in a different-color sugar; set aside.
3. Place five scoops of ice cream on a plate. Freeze until very firm, about 30 minutes.
4. Tint second can of frosting bright yellow. Fill and frost cake layers. With orange icing, pipe a pattern of wide X's around side of cake. With blue icing, pipe dots where X's meet.
5. Top each cookie with a scoop of ice cream, pressing down gently to make scoops adhere. Top each scoop with an ice-cream-cone hat. Freeze 20 minutes, or until ice cream is very firm.
6. Remove from freezer. Working quickly, pipe an orange ruffle around bottom of each cone and a pom-pom at top. Refreeze 10 minutes.
7. With blue icing, pipe eyes and mouths on clown faces and buttons on hats. (Ice-cream clowns can be made up to two days ahead.) Immediately before serving, arrange clown ice-cream cones in a circle on top of cake.