Begin by setting your oven to 350°F (175°C). Lightly coat two 8-inch round cake pans with butter or non-stick spray, then line the bottoms with baking paper.
Add the eggs one at a time, mixing thoroughly after each to maintain a smooth consistency.
In another bowl, blend together the flour and baking powder. Add this mixture gradually to the butter blend, alternating with the milk.
Pour the batter evenly into the prepared pans, gently smoothing the tops with a spatula.
Allow the cakes to cool for 10 minutes in their pans before transferring them to wire racks to finish cooling completely.
While the cakes cool, prepare your frosting. Beat butter until creamy, then slowly incorporate powdered sugar and vanilla. Add milk gradually until the texture is light and spreadable.
Tint the frosting with your chosen pastel shades, dividing it into bowls if using multiple colors.
Apply a thin layer of frosting around the entire cake to trap crumbs. Chill the cake briefly to set.
Finish with a final layer of frosting and decorate with swirls, piped details, sprinkles, or a themed cake topper for a charming girlish touch.