Cake Layers

1. Preheat oven to 350°F (176°C) and prepare two 8-inch cake pans with non-stick baking spray on the sides and parchment paper in the bottom.
2. Add the flour, sugar, baking soda, baking powder and salt to a large bowl and whisk together to combine.
3. Add the eggs, vegetable oil and lemon juice to the dry ingredients and whisk together to combine. Do not over mix.
4. Add the sour cream and whisk together until well combined. Do not over mix.
5. Divide the batter evenly between the prepared cake pans and bake for 22-27 minutes, or until a toothpick comes out with a few moist crumbs.
6. Remove the cakes from the oven and allow to cool for 2-3 minutes, then remove to a cooling rack to finish cooling.

Lemon Curd

1. Combine all the ingredients in a double boiler (or in a metal bowl over a pot of simmering water). Heat while whisking constantly until mixture thickens and reaches 160 degrees, or coats the back of a spoon.
2. Pour the lemon curd into a heat proof bowl, cover with clear wrap pressed onto the top of the curd to avoid a film developing, and refrigerate until cold.

Lemon Buttercream

1. To make the buttercream, add the butter to a large mixer bowl and beat until smooth.
2. Add half of the powdered sugar and mix until well combined and smooth.
3. Add the lemon juice, lemon zest and vanilla extract and salt and mix until well combined and smooth.
4. Add the remaining powdered sugar and mix until well combined and smooth. Add heavy cream, as needed, to get the right consistency of frosting.

To Build the Cake

1. To put the cake together, use a large serrated knife to remove the domes from the top of the cakes, if needed, so that they’re flat. Next, cut each cake horizontally to make 4 layers of cake total. See my tutorial for how to level and torte a cake.
2. To build the cake, place the first layer of cake on a cardboard cake circle or a serving platter. Pipe a dam of frosting around the outer edge of the cake, then fill it with about half of the lemon curd. (For more help with building the cake, see my tutorial for how to fill and stack a layer cake)
3. Add the second layer of cake on top, then spread about 1 cup of lemon buttercream evenly on top.
4. Add the third layer of cake, another dam of frosting and the remaining lemon curd. Top the cake with the final layer of cake.
5. Add a thin (crumb coat) of frosting to the outside of the cake, then place in the fridge to firm up for 1-2 hours. Once the frosting is firm and the cake is a little more steady, frost the outside of the cake. See my tutorial on how to frost a smooth cake with buttercream for help, if needed.
6. Pipe swirls of buttercream on top of the cake with the remaining buttercream, if desired. Add lemon slices, if desired.
7. Refrigerate the cake until ready to serve. Cake is best served cool, but not cold. Store in an air tight cake carrier or well covered. Best if eaten within 3-4 days.