Surprise Inside!
Makes 24 servings
This carousel of color is made from an appliqué of sprinkles and candy decors. Worried about staying inside the lines? Wax paper and a small spoon simplify the process.
1 Preheat the oven to 350°F and prepare four 9-inch round pans (see Please Release Me). Add the rainbow jimmies to the batter and stir well. Divide the batter evenly among the 4 prepared pans. Spread the batter to the edges and smooth the top (see Even It Out). Bake until golden brown and a toothpick inserted in the center comes out clean, 22 to 25 minutes. Transfer the cakes to a wire rack and cool for 10 minutes. Invert, remove the pans, and cool completely.
2 Trim the top of each cake level (see On the Level). Place one cake, trimmed side up, on a cardboard cut to fit (see Getting on Base). Spread ½ cup of the vanilla frosting on top of the cake. Place a second cake on top, trimmed side down, pressing gently on the cake to level. Spread ½ cup of the frosting on top. Repeat the process with a third cake, trimmed side up. Place the last cake, trimmed side down, on top. Spread a thin crumb coating of frosting (see Got Crumbs?) on the cake, filling any gaps, and smooth. Place the cake in the freezer until set, about 30 minutes.
3 Cut a 9-inch circle of wax paper. Fold the circle in half, then in half again into quarters. Now fold in half two more times by bringing the straight edges together. Unfold the wax paper and you have 16 equal-size wedges. Using the fold marks as a guide, cut out the wedges. From a separate sheet of wax paper, cut 16 strips, about 1¾ inches x 5 inches.
4 Place the chilled cake on a work surface. Spread the remaining vanilla frosting on the cake in an even layer and smooth. Use a ruler to find the center of the cake and mark with a toothpick. Arrange the wax-paper wedges in a round on top of the cake, pointing toward the center. Press the strips of wax paper around the sides of the cake vertically, lining up each strip with a wedge on top. Press the wax-paper pieces into the frosting to remove any air bubbles. Return the cake to the freezer for 15 minutes to chill.
5 Work with one color of sprinkles at a time (leaving the white sprinkles for last). Peel 1 wax-paper wedge and the side strip below it from the chilled cake. Using a small spoon, add sprinkles to the frosting on the exposed top and side of the cake, gently pressing to secure, to cover completely (see Sprinkle Appliqué). Brush any excess sprinkles from the cake. Repeat the process on alternate wedges and side strips, using a different color on each set. Take care not to mix the colors in the wedges; remove any stray sprinkles with tweezers. Return the cake to the freezer for 15 minutes to chill before adding the white sprinkles.
6 Remove the remaining wax-paper wedges and side strips and carefully add the white sprinkles (alternating strips of jimmies and nonpareils) on the exposed frosted cake, pressing to secure. Remove any stray sprinkles with tweezers.
7 Place the remaining chocolate sprinkles in a small bowl. Spread the chocolate frosting over the doughnut hole and smooth. Roll the frosted doughnut hole in the sprinkles to cover completely. Place the doughnut hole in the center on top of the cake.