Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans, lining the bottoms with parchment paper.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
Step 3: In a large bowl, using an electric mixer, cream together the softened unsalted butter and granulated sugar until light and fluffy (about 3-5 minutes).
Step 4: Add the eggs one at a time, beating well after each addition. Scrape down the sides of the bowl as needed. Beat in the lemon zest, 1/4 cup fresh lemon juice, and 1 teaspoon vanilla extract.
Step 5: Gradually add the dry ingredients to the wet ingredients in three additions, alternating with the whole milk, beginning and ending with the dry ingredients. Mix on low speed until just combined. Do not overmix.
Step 6: Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.
Step 7: To make the lemon curd: In a small saucepan, whisk together 1/2 cup fresh lemon juice, 1/4 cup granulated sugar, and egg yolks. Cook over medium-low heat, whisking constantly, until the mixture thickens enough to coat the back of a spoon (about 5-7 minutes). Do not boil. Remove from heat and stir in the cold, cubed butter until melted and smooth. Transfer the curd to a bowl, cover with plastic wrap pressed directly onto the surface to prevent a skin from forming, and chill in the refrigerator for at least 1 hour, or until firm.
Step 8: To make the cream cheese frosting: In a large bowl, beat the softened cream cheese and 1/2 cup softened unsalted butter with an electric mixer until smooth and creamy. Gradually add the powdered sugar, mixing on low speed until combined, then increase to medium-high and beat until fluffy. Beat in 1 tablespoon fresh lemon juice, 1 teaspoon vanilla extract, and a pinch of salt.
Step 9: To assemble the cake: If necessary, level the cooled cake layers with a serrated knife. Place one cake layer on your serving plate. Spread half of the chilled lemon curd evenly over the top. Place the second cake layer on top. Spread the remaining lemon curd over the second layer.
Step 10: Frost the top and sides of the cake with the lemon cream cheese frosting. Decorate with additional lemon zest or thin lemon slices, if desired. Chill the cake for at least 30 minutes before serving to allow the frosting and curd to set.