01 - Preheat oven to 350°F. Grease two 9-inch round cake pans and line with parchment paper.
02 - Whisk together flour, baking powder, and salt in a medium bowl. Set aside.
03 - Beat butter and sugar with electric mixer until light and fluffy, about 3-4 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
05 - Alternately add flour mixture and milk to butter mixture, starting and ending with flour. Mix until just combined.
06 - Divide batter evenly between prepared pans. Bake for 28-32 minutes until toothpick inserted in center comes out clean.
07 - Let cakes cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
08 - Beat butter until creamy. Gradually add powdered sugar, milk, vanilla, and salt. Beat until smooth and fluffy, about 3 minutes.
09 - Spread buttercream between cake layers. Frost top and sides with remaining buttercream.