Preheat oven to 350°F (175°C). Grease and line two 4-inch round pans. Whisk flour, baking powder, and salt. Cream butter and sugar, then beat in egg and vanilla. Alternate adding flour mixture and milk until smooth. Divide batter and bake 20-25 minutes until a toothpick comes out clean. Cool completely.

Beat butter for frosting until pale, then sift in powdered sugar in two additions. Add milk and vanilla and beat until stiff peaks form. Divide a third and tint red, black, and yellow.

Level cake layers, fill with white buttercream, and stack.

Apply a thin crumb coat of white buttercream and chill 25 minutes.

Frost with a final thick white layer. Pipe or outline the One Piece Jolly Roger on top with black, then fill with red and yellow. Serve or keep chilled.