- 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.