Preheat oven to 350°F (175°C) and butter two 9 inch pans with parchment liners. Cream 1 cup butter and sugar until fluffy, about 3 minutes, then add eggs one at a time and vanilla.

Whisk flour, baking powder, soda, and salt. Add to butter mixture in three additions, alternating with buttermilk, starting and ending with dry. Divide batter between pans and bake 30 to 35 minutes until a toothpick is clean. Cool 10 minutes in pans, then invert onto a rack.

Beat 2 cups frosting butter until pale. Add powdered sugar gradually, then vanilla and 3 tablespoons cream. Beat on medium 4 minutes. Reserve 1 cup white, tint some red, some blue, and a small amount skin tone with gel coloring.

Set one layer bottom side up, spread with white buttercream, top with second layer bottom up. Crumb coat with white buttercream and chill 20 minutes. Spread red on sides, blue on top third, and smooth.

Pipe the Mario face on wax paper using skin tone, white, and black buttercream. Freeze 15 minutes, then press onto cake. Pipe white border on base, red border on hat, and add the red “M” inside a white circle on the blue cap.