You make a birthday cake by preparing a classic sponge cake using flour, sugar, butter, eggs, and milk, then baking it until golden and fluffy. Once the baked cake layers cool completely on a wire rack, apply a smooth layer of buttercream frosting between the tiers and over the exterior. Decorate the finished dessert with colorful sprinkles, piped icing borders, and festive birthday candles on top. Personalizing the cake with the guest of honor favorite colors makes the celebration extra special.