You can make this cake with 3 or 4 cake pans. If you prefer equal amounts of cake to frosting (me!) use 4 cake pans and decrease baking time to 20 minutes. More traditionally, you can use 3 cake pans.
1 cup (2 sticks) butter, softened
2 cups granulated sugar
5 eggs, room temperature
2 tsp vanilla extract
3 cups all-purpose flour
1/2 tsp baking powder
1/4 tsp salt
1 cup buttermilk, room temperature
Preheat oven to 350º F. Butter or spray with baking spray, three (or four) 9-inch round cake pans. Cut parchment paper in circles the same size as bottom of cake pan and place in cake pans. Spray again with cooking or baking spray.
Using electric mixer, with paddle attachment, cream together butter and sugar until light and fluffy. Add eggs one at a time, fully incorporate each egg before adding another. Add vanilla.
In large bowl sift together flour, baking powder & salt.
Add dry mixture to butter and sugar mixture alternately with buttermilk, beginning and ending with dry ingredients. Beat cake batter on high speed for about 5 seconds to fully incorporate all ingredients. Scrape down sides and bottom of bowl, making sure to have all ingredients mixed well.
Pour cake batter between the prepared cake pans and bake for 25-30 minutes if using 3 cake pans (20 minutes if using 4 cake pans) or until a toothpick inserted in the center comes out clean. Remove and allow to cool slightly in cake pans for about 10 minutes. Take a knife and go along edges between cake pan and cake, to loosen cake, to make removal easier. Flip cake over into your hand or another sheet pan, and then flip cakes over onto wire rack so domes are up, and allow to cool completely.