Prepare the Cake Batter:

1. Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.
2. In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
3. In a large mixing bowl, beat unsalted butter and granulated sugar together until light and fluffy, about 3-4 minutes.
4. Add eggs one at a time, beating well after each addition.
5. Mix in lemon zest and fresh lemon juice.
6. Gradually add the dry ingredients to the butter mixture, alternating with buttermilk and sour cream. Begin and end with the dry ingredients, mixing until just combined.

2. Bake the Cake Layers:

1. Divide the batter evenly between the prepared pans.
2. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
3. Cool the cakes in their pans for 10 minutes before transferring them to a wire rack to cool completely.

3. Make the Frosting:

1. In a large bowl, beat softened butter and cream cheese together until smooth and creamy.
2. Gradually add powdered sugar, mixing until fluffy.
3. Mix in lemon zest and fresh lemon juice until fully incorporated.

4. Assemble the Cake:

1. Place one cake layer on a serving plate. Spread a generous layer of lemon curd filling over the top.
2. Add the second cake layer and gently press down.
3. Use the cream cheese frosting to cover the top and sides of the cake.

5. Garnish and Serve:

1. Decorate the cake with lemon slices or zest for a vibrant finish.
2. Chill the cake for 30 minutes before slicing for clean cuts.
3. Slice and serve to your delighted guests.