To Make the Lemon Curd:

1. Add lemon juice, lemon zest, sugar, kosher salt, and eggs to a medium bowl.  Whisk well to combine before turning on the heat.
2. Add the butter and heat the mixture over medium heat, stirring at regular intervals.  This is a slow process; best not to rush it or you’ll scramble the eggs and get a gritty, grainy curd. The curd should reach the consistency of loose pudding on the stovetop.
3. When the mixture coats the back of a spoon, it is done. 
4. Remove immediately to a non-reactive bowl.  Use a fine mesh strainer to remove any remaining bits or chunks in the curd.
5. Cover the top of the curd immediately with plastic wrap and place in the refrigerator. Allow to cool completely before using to fill your cake.

To Make the Cake:

1. Set your oven to a true 325°F.  An oven thermometer is very useful to help you determine whether your oven is at the correct temperature.
2. Combine the sugar, vanilla beans (if using) and lemon zest in a medium bowl or deli cup.  Use your fingers to scrunch the combination together (or, alternatively, put the top on the deli cup and shake away!) until the mixture is combined.  The sugar will get clumpy from the release of the oils in the lemon zest, and that is a great thing!
3. Add the sour cream and lemon juice to a small bowl or deli cup.  Stir to combine.
4. Sift cake flour, baking soda, cornstarch, and kosher salt in a medium bowl and set aside.
5. Add room-temperature butter and oil to a large mixing bowl, or to the bowl of a stand mixer.  Mix until combined.  Add the sugar/vanilla/lemon mixture and cream the butter and sugar until light and fluffy, scraping the bowl regularly to ensure even mixing.
6. Add the eggs, one at a time.  Add the next egg only once the previous egg has been fully incorporated.
7. Add the pure vanilla extract (if using) and mix thoroughly to combine.  Scrape the bowl regularly to ensure even mixing.
8. Add half of the flour mixture and mix until nearly combined.
9. Add all of the sour cream/lemon juice mixture and mix until nearly combined.
10. Add the other half of the flour mixture and mix until nearly combined.  Scrape the sides and bottom of the bowl, and then gently fold the mixture together until it is fully combined.
11. Prep three 8” cake pans (I use butter and flour to do this).  Fill each cake pan with 1/3 of the batter.
12. Bake for 20-27 minutes, or until an instant-read thermometer reads 205°F in the center of the cakes.
13. Allow the cakes to cool on cooling racks for 5-7 minutes, then turn place the cakes onto cooling racks to finish cooling.

To Make the Cream Cheese Frosting:

1. Add the room-temperature butter to the bowl of your stand mixer, or a large mixing bowl.  Mix with the flat beater attachment until very smooth.
2. Add the cream cheese, vanilla beans, and lemon zest and blend together until smooth.
3. Add fine sea salt and 1.5 cups of the confectioner’s sugar.  Blend on low speed until there is no evidence of the confectioner’s sugar.  Add the confectioner’s sugar, 1.5 cups at a time, and repeat the process of blending until the confectioner’s sugar is invisible each time.
4. Once the confectioner’s sugar is completely incorporated, blend on medium speed until the frosting has notably increased in volume, about 2-4 minutes. 
5. You can use immediately, or you can refrigerate and re-whip when ready to use.  This frosting should be slightly softer than American Buttercream, but it should still pipe-able with the Wilton star piping tip! 
6. To build the cake, place a generous amount of frosting on the bottom layer. Create a dam around the outer edge of the cake, and fill with a couple of tablespoons of lemon curd.  Repeat the process with the second layer, then cover the entire cake in a thin coat of frosting.  If you’re making a naked cake, you’re done! If not, you’ve completed the crumb coat.
7. When building the cake, make sure to do a crumb coat before doing the final frosting layer, and allow the crumb-coated cake to stay in the refrigerator for at least four hours (preferably 8) before finishing. Also, after crumb coating, I put four dowels in the middle to stabilize while the crumb coat is setting in the refrigerator.
8. Enjoy!