Preheat oven to 350 degrees. Line 3 - 9" round cake pans with waxed paper. Spray each with baking spray to coat.
Prepare Your Ingredients
Using a fine-edged grater, zest 2-3 lemons, enough to measure 6 teaspoons. Using a citrus juicer, squeeze lemons for 5 tablespoons of juice.
Prepare the Cake Batter
In a large mixing bowl, cream together the softened butter, vegetable shortening, sugar, and lemon zest until light and fluffy.
Add eggs, one at a time, beating well after each addition. Stir in lemon juice and vanilla extract.
In a small bowl, sift together the all-purpose flour, baking powder, baking soda, and salt to combine.
Add the flour mixture to the creamed mixture alternately with buttermilk, beginning and ending with dry ingredients.
Equally pour the batter into the three prepared cake pans. Lightly tap each pan once to remove any air bubbles.
Bake in preheated oven for 25-28 minutes or until cake tests done with a toothpick inserted in the center that comes out clean.
Cool for 10 minutes before removing to wire racks to cool completely.
Making the Buttercream Frosting
In a large mixing bowl, cream the softened butter until light and fluffy.
Add the lemon juice, heavy cream, and lemon zest, mixing well.
Gradually add the powdered sugar, one cup at a time. Beat until frosting has desired spreading consistency. If the frosting seems too thick, add 1 tablespoon milk. If too thin, add 1/2 cup more powdered sugar.
Spread frosting between cooled cake layers and over the top and sides of cake. Makes 12-16 servings.
Notes
*Unless otherwise indicated, all butter used on this recipe site is salted.