01 - Preheat oven to 350°F. Grease two 9-inch round cake pans and line bottoms with parchment paper.
02 - Whisk together flour, baking powder, and salt in a medium bowl until well blended. Set aside.
03 - Beat softened butter and granulated sugar with electric mixer on medium-high speed until light and fluffy, approximately 3-4 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla extract until incorporated.
05 - Alternate adding flour mixture and milk to butter mixture, beginning and ending with flour. Mix until just combined; avoid overmixing.
06 - Divide batter evenly between prepared pans. Smooth tops with spatula for even baking.
07 - Bake for 28-32 minutes until toothpick inserted into center comes out clean.
08 - Let cakes cool in pans for 10 minutes, then remove to wire racks to cool completely before frosting.
09 - Beat butter until creamy. Gradually incorporate powdered sugar, milk, vanilla extract, and salt. Beat until smooth and fluffy, about 3 minutes.
10 - Place one cooled cake layer on serving plate. Spread buttercream evenly over top. Position second layer and frost top and sides with remaining buttercream.