This caterpillar, made by arranging cupcakes in a curve, makes a memorable arrangement for a baby's first birthday. One jumbo cupcake is used for the head, and more standard cupcakes make up the body.
Make cupcakes: Preheat oven to 350 degrees. Line 28 cups of standard muffin tins and 1 cup of a jumbo muffin tin with paper liners. Whisk together flour, cocoa, baking soda, and salt.
With an electric mixer on medium-high speed, cream butter and granulated sugar until pale and fluffy. Add brown sugar, and beat until fluffy. Add eggs, one at a time, beating until well incorporated, scraping down sides of bowl as needed. Mix in sour cream. Reduce speed to low. Add flour mixture in three batches, alternating with two additions of buttermilk, and mixing until just combined after each.
Divide batter evenly among prepared cups, filling each three-quarters full. Bake, rotating tins halfway through, until tops are firm to the touch and a cake tester inserted in centers comes out clean, 25 to 30 minutes. Transfer tins to wire racks to cool completely before removing cupcakes. Cupcakes can be stored overnight at room temperature, or frozen up to 2 months, in airtight containers.
Decorate cupcakes: Tint fondant with green gel-paste food color, and roll out to 1/8 inch thick on a work surface lightly dusted with cornstarch. Using cookie cutters, cut out one 4 1/2-inch round and twelve 3 3/4-inch rounds. Divide 2 cups buttercream into two bowls; tint half yellow and half pale blue with gel-paste food colors. Transfer to pastry bags fitted with small plain tips (No. 3). Tint 1/4 cup buttercream red; transfer to a pastry bag fitted with a fine plain tip (No. 1). Spread cupcakes with a thin layer of plain buttercream, and transfer remaining untinted buttercream to a pastry bag fitted with another small plain tip (No. 2). Place a fondant round on top of each cupcake, pressing gently to adhere, and mold to fit smoothly.
To make the head, pipe two yellow dots for the eyes on top of jumbo cupcake, then pipe tiny white dots for pupils. Using a skewer or toothpick, poke two holes above eyes, and insert mini candy canes into holes for antennae. Use red buttercream to pipe the mouth. Pipe dots all over other half of cupcake, alternating between yellow and pale-blue buttercreams. Continue to pipe yellow and blue dots all over remaining cupcakes, then pipe tiny white dots on top of each. Refrigerate 30 minutes to allow frosting to set. Cupcakes can be stored up to 1 day at room temperature in airtight containers.
Arrange 12 standard cupcakes side by side in a curving line, with the jumbo cupcake at the front. Serve remaining cupcakes as desired.
Cupcakes can be stored up to 1 day at room temperature in airtight containers.