Preheat your oven to 350°F. Grease and flour two 9-inch round cake pans. You can also line the bottoms with parchment paper for easy removal.

In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined.

Add the softened butter to the dry ingredients, and using an electric mixer on low speed, mix until the mixture resembles coarse crumbs.

Whisk together the egg, egg whites, buttermilk, lemon juice, lemon zest, and vanilla extract in a separate bowl.

Gradually add the wet ingredients to the dry mixture, mixing on medium speed until the batter is well combined.

Divide the batter evenly between the prepared cake pans.

Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Remove the cakes from the oven and let them cool in the pans for 10 minutes. Then, carefully transfer them to a wire rack to cool completely.

In a large mixing bowl, beat the softened cream cheese, vanilla extract, fresh lemon juice, and butter together with an electric mixer until smooth and creamy.

Gradually add the powdered sugar, mixing on low speed after each addition until fully incorporated.

After the cake layers have cooled completely, place one cake layer on a flat surface, such as a cutting board or cake turntable.

Using a long knife, carefully slice off any dome-shaped top from the cake layer. Hold the knife parallel to the surface of the cake and make a gentle sawing motion to level it. You can also rotate the cake while cutting to ensure an even level.

Repeat the same process with the second cake layer so both layers have flat tops.

You can use the excess cake trimmings for snacking or save them to make cake pops or a trifle dessert.

Now, you have two even and flat cake layers ready to be assembled with the cream cheese frosting.

Place two pieces of parchment paper overlapping each other in the center of a serving plate or cake stand. This will help keep the serving platter or cake stand clean, and they will slide out easily after decorating the cake.

Place one cake on top of the parchment paper.

Spread a generous layer of cream cheese frosting over the top of the first cake layer.

Carefully place the second cake layer on top.

Frost the entire cake with the remaining cream cheese frosting. You can decorate the cake with lemon zest on top for an extra touch.

Remove the parchment paper carefully by sliding them out slowly.

Store the cake in the refrigerator until you're ready to serve.