Preheat your oven to 350°F (175°C) and line your 4-inch cake pan with parchment paper to prevent sticking.

In a medium bowl, cream together the softened butter and sugar until light and fluffy, about 3-5 minutes.

Add the egg and vanilla extract, mixing until fully incorporated and smooth.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry mixture to your wet ingredients, alternating with the milk. Mix just until combined to avoid overmixing.

Pour the batter into your prepared pan, smoothing the top with a spatula to create an even surface.

Bake for 22-25 minutes, or until a toothpick inserted into the center comes out clean. Look for a golden top and a slight spring back when gently pressed.

Allow your cake to cool in the pan for about 10 minutes before transferring it to a wire rack.

Once cooled, use a serrated knife to level the top if it has domed during baking, then slice the cake horizontally into 2-3 even layers.

For the frosting, beat the softened butter in a large bowl until creamy. Gradually add the powdered sugar and vanilla extract, mixing in the heavy cream until the frosting is light and fluffy.

Set aside 1/3 of the frosting for the exterior of the cake. Divide the remaining frosting into bowls and add different food coloring as desired.

Layer your cake by spreading a thin layer of frosting between each cake layer, then apply a crumb coat over the entire cake.

Once the crumb coat has set, apply a final layer of frosting to smooth out the surface.

Use colored frosting in piping bags to create designs or messages on the cake. Decorate with edible markers, sprinkles, small candies, or fresh berries as desired.