Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large bowl, whisk together flour, baking powder, baking soda, and salt.

In a separate bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla.

Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined.

Divide batter evenly between the prepared pans and bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let cakes cool in pans for 10 minutes before inverting onto a wire rack to cool completely.

In a medium bowl, beat together cream cheese, powdered sugar, and vanilla extract until smooth.

In a large bowl, beat butter until smooth. Gradually add powdered sugar, alternating with milk, until frosting reaches desired consistency. Stir in vanilla.

Place one cake layer on a serving plate and spread with half of the cream cheese filling.

Top with the second cake layer and spread with the remaining cream cheese filling.

Frost the top and sides of the cake with the buttercream frosting.