In a saucepan, add all the ingredients except the butter. Cook over medium heat, whisking continuously until the mixture starts simmering and thickens.

Remove from the heat and add the butter. Mix until it has melted and is fully incorporated.

Pass through a sieve to remove the zest, cover with plastic wrap (making sure it touches the mixture), and refrigerate until cold.

Into a large bowl, add the egg yolks, milk, lemon juice, lemon zest, vanilla extract, and oil. Whisk well.

Sift in the flour and salt. Whisk until well combined and no dry ingredients are left.

In the bowl of a stand mixer fitted with a whisk attachment (or using a hand mixer and a bowl), add the egg whites and cream of tartar. Whip on medium-low speed, gradually adding sugar. When all the sugar is added, switch the speed to medium-high and whip to medium peaks. Do not overwhip to stiff peaks!

Using a rubber spatula, fold ⅓ of the egg white mixture into the egg yolk mixture until well combined.

Then, add the rest of the egg whites and gently fold until a homogeneous consistency.

Pour the cake batter onto the prepared baking sheet and spread it in an even layer using an offset spatula forming an 11” by 16” (28cm by 40cm) rectangle. Bake the sponge for 25 minutes or until the top is springy to the touch. A toothpick inserted into the center should come out clean.

Remove from the oven and let it rest for 10 minutes. Then, lift the cake from the pan, holding onto the parchment paper, and flip it onto a fresh piece of parchment paper. Peel the paper and cover the sponge with plastic wrap.

Allow the sponge to cool to room temperature. Cut the sponge into two 8” by 11” (20cm by 28cm) rectangles.

Place all the ingredients into the bowl of a stand mixer fitted with a whisk attachment (or use a hand mixer) and whisk on low until no dry powdered sugar is left.

Then, whisk on medium until reaching a homogeneous consistency.

Scrape the sides of the bowl and whisk once again on high until thick and fluffy. Add the cold lemon curd and whip just until combined. The whole process should take 1-2 minutes. Be careful not to overwhip the cream.

Assembling the cake

Place the first cake layer inside the baking dish.

Spread half of the cream in an even layer on top of the sponge. Place the second sponge layer on top.

Spread the rest of the cream on top. Decorate the top as desired and refrigerate for at least 4 hours before serving.