Prepare the oven: Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
Prepare dry ingredients: In a medium bowl, sift together the cake flour, baking powder, baking soda, and salt. Set aside.
Cream butter and sugar: In a large mixing bowl, beat the softened butter and sugar together with an electric mixer on medium speed until light and fluffy (about 3-4 minutes).
Add eggs and vanilla: Add eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Alternate adding dry ingredients and sour cream: Gradually add the dry ingredients in three parts, alternating with the sour cream. Begin and end with the dry ingredients. Mix until just combined.
Bake the cake: Divide the batter evenly between the two prepared pans. Smooth the tops with a spatula. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.
Cool the cakes: Let the cakes cool in the pans for 10 minutes, then turn them out onto a cooling rack to cool completely.
Make the buttercream frosting: Beat the softened butter in a mixing bowl until creamy. Gradually add the powdered sugar, vanilla extract, and heavy cream, one tablespoon at a time, until you achieve a smooth, spreadable consistency.
Frost the cake: Once the cakes have cooled, spread a layer of frosting on top of one cake. Place the second cake on top and frost the top and sides of the entire cake.
Serve and enjoy! Let the cake sit for a few minutes to set the frosting, then slice and serve.