1. Preheat the oven to 350°F and grease two 8-inch or 9-inch round cake pans. Line the bottoms with parchment paper.

2. In a medium bowl, whisk together the flour, baking powder, and salt.

3. In a large mixing bowl, beat the butter and granulated sugar until light and fluffy.

4. Add the eggs one at a time, beating well after each addition.

5. Mix in the lemon zest, lemon juice, and vanilla extract.

6. Add the dry ingredients in three additions, alternating with the milk and sour cream, and mix just until combined.

7. Divide the batter evenly between the prepared pans and smooth the tops.

8. Bake for 22 to 28 minutes, or until a toothpick inserted in the center comes out clean.

9. Let the cakes cool in the pans for 10 minutes, then transfer them to wire racks to cool completely.

10. To make the frosting, beat the cream cheese and butter until smooth and creamy.

11. Add the powdered sugar gradually, then mix in the lemon zest, lemon juice, and heavy cream until fluffy.

12. Place one cake layer on a serving plate, spread frosting over the top, then add the second layer.

13. Frost the top and sides of the cake, then chill for 20 to 30 minutes before slicing for cleaner pieces.