Make the Cake

1. Preheat the oven to 350°F (176°C). Line three 8-inch cake pans with parchment paper in the bottom and grease the sides.
   Combine the flour, baking soda, baking powder and salt in a medium sized bowl. Set aside.
2. Cream the butter and sugar in a large mixer bowl on medium speed for about 2-3 minutes, until light and fluffy.
3. Add the egg whites and vanilla extract and mix until well combined. Scrape down the sides of the bowl, as needed, to make sure everything is combined.
4. Add about one-third of the flour mixture to the batter and beat on medium speed until incorporated.
5. Add about half of the milk and the lemon juice and zest and beat on medium speed until incorporated.
6. Continue alternating adding dry and wet ingredients, scraping down the sides of the bowl as needed, and beating until incorporated after each addition. There should be three total additions of dry ingredients and two total additions of milk. End with the dry ingredients.
7. Divide the batter evenly between the cake pans.
8. Bake the cakes for 25-30 minutes, or until a toothpick inserted into the middle of the cakes comes out clean. Don’t be alarmed if the tops are a little browned, that is normal.
9. Remove the cakes from the oven and allow to cool for 1-2 minutes, then remove to a cooling rack to cool completely.

Make the Buttercream

1. Add the butter to a large mixer bowl and beat until smooth.
2. Slowly add about half of the powdered sugar, mixing until well combined and smooth.
3. Add the salt, vanilla, lemon zest and lemon juice and mix until well combined and smooth.
4. Slowly add the remaining powdered sugar and mix until well combined and smooth.
5. Add additional lemon juice, if needed, to thin out the frosting.

Make the 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 170-180 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 the top of the curd to avoid a film developing, and refrigerate until cold and firm.

Make the Bavarian Cream

1. In a small bowl, sprinkle the gelatin onto the lemon juice and set aside.
2. In a medium bowl, whisk the egg yolks together and set aside.
3. Add 3/4 cup of the the heavy whipping cream, sugar, vanilla extract, lemon zest to a large saucepan and heat over medium heat until warm.
4. Remove the cream mixture from heat and slowly pour the hot cream into the eggs to temper them.
5. Add the egg and cream mixture back into the saucepan and return to the heat. Continue cooking over medium heat until the mixture is thick enough to coat the back of a spoon, or reaches about 160°F. It should happen fairly quickly.
6. Add the gelatin mixture to the hot cream and stir until smooth.
7. Pour the custard into another bowl and set that bowl inside another bowl over ice. Allow to cool to room temperature.
8. While the custard cools, add the remaining cup of heavy whipping cream and powdered sugar to a large mixer bowl and whisk on high speed until stiff peaks form.
9. When the custard is ready, gently fold the whipped cream into the custard. Be sure it’s at least room temperature, so the whipped cream doesn’t wilt/melt.

Assemble

1. The cake layers should be pretty flat, but if there’s a dome, trim the tops of the cakes so they are flat. Cut each cake in half, so that you end up with 6 layers of cake. Get the lemon curd and bavarian cream from the fridge and stir them until smooth. The bavarian cream may need a little hand whisking to work out any lumps.
2. Place the first layer of cake on a serving platter. Pipe a small dam of frosting around the outer edge.
3. Fill the dam with 1/3 of the bavarian cream.
4. Place the second layer of cake on top of the cream. The cake layers are very tender, so I recommend using a cake lifter.
5. Add another dam of frosting around the out edge of the cake. Fill the dam with about half of the lemon curd.
6. Repeat with another layer of cake, dam of frosting and 1/3 of the bavarian cream.
7. Repeat with another layer of cake, dam of frosting and 1/2 of the lemon curd.
8. Repeat with the another layer of cake, dam of frosting and remaining 1/3 of the bavarian cream.
9. Add the final layer of cake on top, then frost the outside of the cake with a crumb coat and refrigerate for at least 2-3 hours for the cake to firm up.
10. Frost the outside of the cake and decorate as you wish. To create the watercolor look I used, frost the outside of the cake roughly, then color the remaining frosting with yellow gel icing color. Place a few blobs of yellow frosting around the outside of the cake, then smooth out the cake a few more times to spread the yellow frosting around and create the effect. Use the remaining yellow frosting to pipe around the edges.
11. Refrigerate the cake until ready to serve. The cake is best when stored in an air tight container and eaten within 3-4 days.