1/2 cup unsalted butter, softened (plus extra for greasing the pans)
1 1/2 cups sugar
3 large eggs
2 1/4 cups all-purpose flour
1 teaspoon salt
3 1/2 teaspoons baking powder
1 1/4 cups whole milk
1 teaspoon vanilla
2 1/2 cups buttercream frosting, such as basic buttercream