Isabel's Lemon Birthday Cake

1. Make the cakes 1 day in advance: Position a rack in the center of your oven and preheat the oven to 325°F. Butter three 9-inch round cake pans and line the bottom and sides with parchment paper.
2. Sift the flour, baking powder, and salt into a large mixing bowl. Set aside.
3. In a separate bowl, combine the egg yolks with the sugar and beat vigorously with a whisk until very light in color and creamy looking; you can use an electric mixer for this step if you want. Add ½ cup of the lemon curd, the olive oil, ½ cup (118ml) warm water, and the lemon zest. Whisk until well combined.
4. Make a well in the center of the dry ingredients and add the wet ingredients. Fold the batter together until no dry bits of flour remain.
5. Put the egg whites into the bowl of an electric mixer fitted with the whisk attachment and beat on medium speed until soft, glossy peaks form, about 3 minutes.
6. Incorporate the egg whites into the batter in three additions, folding gently after each addition. Carefully divide the batter between the three prepared pans. Bake for 20 minutes, rotate the pans, and continue to bake until a cake tester inserted into the centers of the cakes comes out clean and the tops are very lightly browned, about 10 additional minutes. Remove the cakes from the oven and place on a wire rack. Allow the cakes to cool completely in their pans before removing them and removing the parchment paper.
7. Wrap each cake layer in plastic and freeze the layers for at least 4 hours or preferably overnight.
8. Make the frosting: Place the butter and lemon zest in the bowl of an electric mixer fitted with the paddle attachment. Beat on medium speed for 5 minutes, or until the butter is super shiny and smooth and smells intensely of lemon.
9. While the butter mixes, sift the confectioners' sugar into a medium bowl. Scrape down the bottom and sides of the mixer bowl and add one- third of the confectioners' sugar. Mix on low speed until the sugar has been fully incorporated. Scrape down the bottom and sides of the bowl and add the remaining two-thirds of confectioners' sugar; mix on low speed until all the sugar has been mixed in.
10. Once all the sugar has been incorporated, add the milk and beat on medium-low speed for 5 minutes, until smooth and billowy. The frosting can be stored at cool room temperature in a sealed container for 1 day. If your kitchen is very warm, store the frosting in the fridge and remove it 4 hours before you plan on assembling the cake.
11. Assemble the cake: When you are ready to assemble and decorate the cake, remove the layers from the freezer and remove the plastic wrap. Place 1 layer of cake on a serving plate or cake board and spread with ¼ cup of the lemon curd, leaving a 2½-inch ring of cake uncovered at the edge.
12. Place your second cake layer on top of the first and repeat with the remaining¼ cup lemon curd. Place the top layer on the cake, and gently press down on the center of the cake just a little bit.
13. Scoop a generous spoonful of frosting onto the top layer and spread it out and down the sides. Repeat until you have covered the cake. Use the back of a spoon or an offset spatula to swoop and swirl the frosting however you'd like. Decorate with edible flowers, candied lemon zest, and/or shredded coconut, as desired.
14. Store the cake in the fridge until 20 minutes before you are ready to serve it. It will keep well in a sealed container in the fridge for 1 week or in the freezer for 1 month (omit the flowers and other decoration until ready to serve, and defrost in the fridge overnight).

Lemon Curd

Use the best-quality peppery olive oil you can find for this curd. Because it has less butter, the finished product is slightly softer at room temperature than versions made with all butter, and the lemon flavor punches harder without the extra dairy. The corn- starch adds an extra measure of stiffness, so that the curd oozes a little bit less when it sits between cakes, and holds a perkier bead.

1. Fill a large bowl with ice cubes and cold water. Place a clean heatproof bowl inside it.
2. Combine the sugar, eggs and yolks, lemon zest, lemon juice, and cornstarch in a 2-quart heavy-bottomed saucepan and whisk them together. Cook over medium heat, stirring frequently with a wooden spoon or heatproof silicone spatula, until warm. Add the olive oil and butter and cook, stirring frequently, until the curd is thick enough to coat the back of the spoon, about 8 minutes.
3. Transfer the lemon curd to the bowl set inside the ice bath and cover with plastic wrap touching its surface. Chill until cold, at least 1 hour. Store in a sealed container in the fridge for up to 1 week.

note: You can substitute store-bought lemon curd if you are short on time and do not want to make your own from scratch. You will need approximately 16 ounces.

The cake layers should be made 1 day in advance to allow the cakes to freeze completely. It's best to freeze the cakes overnight before frosting them, as it makes the crumb more compact and easier to finish, and you can keep the cakes frozen for up to 2 weeks. This also makes frosting the cake much easier and results in a cleaner cake slice with defined layers. The frosting and filling should also be made in advance and can be stored, separately, for up to 1 week.