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

Prepare the Lemon Cake Batter: In a medium bowl, whisk together flour, baking powder, and salt. Set aside. In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy (about 3 minutes). Add eggs one at a time, mixing well after each. Stir in vanilla, lemon zest, and lemon juice. Gradually add the dry ingredients, alternating with milk and sour cream, beginning and ending with the dry ingredients. Mix until just combined.

Bake the Cake: Divide the batter evenly between the prepared pans and bake for 25-30 minutes, or until a toothpick inserted comes out clean. Let the cakes cool in the pans for 10 minutes, then remove them and transfer to a wire rack to cool completely.

Make the Lemon Cream Filling: Beat the heavy cream until stiff peaks form, then set aside. In another bowl, beat the softened cream cheese until smooth. Add powdered sugar, lemon juice, lemon zest, and vanilla. Mix until combined, then gently fold in the whipped cream until smooth and fully incorporated.

Prepare the Lemon Frosting: Beat the powdered sugar and butter together until smooth. Gradually add the lemon juice and zest and continue mixing until the frosting is smooth and spreadable.

Assemble the Cake: Place one layer of cake on a serving plate. Spread a generous layer of lemon cream filling on top. Add the second cake layer, pressing down gently to secure.

Frost the Cake: Spread the lemon frosting evenly over the top and sides of the cake.

Chill and Serve: Refrigerate the cake for at least 1 hour to set the layers and flavors. Slice and serve chilled.