01 - Preheat oven to 350°F. Grease two 9-inch round cake pans and line with parchment paper.
02 - Whisk flour, baking powder, and salt in a medium bowl. Set aside.
03 - Beat butter and sugar with electric mixer until light and fluffy, approximately 3-4 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
05 - Alternate adding flour mixture and milk to butter mixture, beginning and ending with flour. Mix until just incorporated, avoiding overmixing.
06 - Distribute batter evenly between prepared pans. Smooth surfaces using spatula.
07 - Bake for 28-32 minutes until toothpick inserted in center emerges clean.
08 - Let cakes rest in pans for 10 minutes, then invert onto wire racks to cool completely.
09 - Beat butter until creamy. Gradually incorporate powdered sugar, milk, vanilla, and salt. Beat until smooth and fluffy, about 3 minutes.
10 - Spread buttercream between cooled cake layers. Frost top and sides with remaining buttercream.