Preheat your oven to 350°F (175°C) and line a 4-inch round cake pan.

Cream butter and sugar until light and fluffy (about 3 minutes). Add egg and vanilla, and mix well.

In a separate bowl, whisk flour, baking powder, and salt. Gradually add the dry mix to the wet mix, alternating with the milk.

Pour into the prepared pan, smooth the top, and bake for 22–25 minutes until a toothpick comes out with a few moist crumbs.

Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Once cooled, level the cake top and slice horizontally into 2–3 layers.

Beat butter until creamy. Add powdered sugar, cream, and vanilla. Beat for 5 minutes.

Set aside 1/3 of the frosting for the outer layer; color the rest as desired.

Spread frosting between layers and apply a crumb coat. Chill for 15 minutes.

Apply the final frosting layer and decorate as desired, topping with sprinkles or berries if desired.