Preheat oven to 350°F (180°C). Grease and line two 4-inch round pans. Whisk flour, baking powder, baking soda, and salt. In another bowl, beat butter and sugar until fluffy, then beat in egg and vanilla. Add flour mixture in three additions alternating with milk, mixing just until combined.

Divide batter between pans and bake 20-25 minutes until a toothpick comes out clean. Cool in pans 10 minutes, then transfer to a wire rack to cool completely.

Beat 1 cup butter until creamy. Gradually add 2 cups powdered sugar, then cream and vanilla; beat 3 minutes until fluffy. Tint portions white, black, purple, and pink.

Level cake layers if needed. Stack with a layer of white buttercream, then apply a crumb coat and chill 15 minutes. Frost with a smooth white coat for the skull base.

Using a small round tip, pipe the black hood, eyes, nose, and mouth. Add a purple jester's hat, pink cheeks, and a small flower on the hat. Serve or chill until ready.