Preheat oven to 350°F (175°C). Grease and line cake pans or bowl.
In a bowl, whisk flour, baking powder, and salt.
In another bowl, beat butter and sugar until light and fluffy.
Add eggs one at a time, mixing well after each.
Mix in vanilla extract.
Add dry ingredients alternately with milk, mixing until smooth.
Divide batter evenly into pans or pour into bowl.
Bake for 35 to 40 minutes, or until a toothpick comes out clean.
Let cakes cool completely on a rack.
Once cooled, trim cake tops to level.
Stack layers using a small amount of frosting between them.
Shape the cake gently into a soft skirt silhouette using a knife.
Wrap the lower half of the Barbie doll in plastic wrap.
Create a small hole in the center of the cake.
Insert the doll carefully so it stands upright.
Beat butter until creamy.
Gradually add powdered sugar.
Mix in vanilla and milk until smooth and spreadable.
Divide frosting and tint with food coloring if desired.
Apply a thin crumb coat over the cake.
Fill a piping bag with buttercream.
Pipe swirls or stars from bottom to top to form the dress.
Add sprinkles if using.
Chill briefly before serving if needed.
