9 egg yolks (reserve the whites for Swiss meringue recipe below)
1 cup lemon juice
1 cup sugar
4 ounces butter (1 stick)
1 cup softened butter (2 sticks) plus extra for the cake pans
3 cups all-purpose flour plus extra for the cake pans
1 tablespoon baking powder
2 cups sugar
6 whole eggs
1 cup milk
2 cups egg whites, reserved from lemon curd
3 cups sugar
1 teaspoon lemon juice
Lemon curd: Combine all the ingredients in a double boiler set over medium heat. Bring the water barely to a simmer and cook, stirring frequently, until the mixture thickens (it should reach 130 to 140 degrees, and it should form a thick coating on the back of a spoon). Pour into a nonreactive container to cool; cover and refrigerate. The curd will thicken as it cools. (May be made up to a week ahead and kept refrigerated.)
Cake: Preheat the oven to 350 degrees. Butter and flour two 9-inch cake pans. Sift the flour and baking powder together. Put the butter and sugar in the bowl of a mixer fitted with a paddle, and cream together on high speed until white and fluffy, about 6 to 7 minutes. Reduce the speed to low and add the eggs one at a time, beating until combined (do not overbeat). Add the flour mixture and milk alternately in several batches. Mix until thoroughly combined, taking care not to overbeat.
Pour batter into cake pans, and bake for 30 to 40 minutes, until the cakes are golden around the edges and the center springs back from the touch or a toothpick comes out clean.
Swiss meringue: Place egg whites, sugar, and lemon juice in a mixing bowl, and place the bowl over a simmering water bath, making sure the water remains hot but not boiling. Whisk on medium speed until the mixture is warm and the sugar crystals have dissolved. Continue whisking for 10 minutes. Transfer the meringue to a food mixer, and continue whisking on medium speed for 15 minutes, until meringue is thick.
Assembly: Slice each cake in half horizontally to form four layers, and spread the lemon curd between them. Using a spatula, spread a thin layer of meringue over the entire cake. Pile the remaining meringue on top until it's tall and pretty. To serve, slice and garnish with candied citrus rinds.
Optional: Light a small kitchen blowtorch and very quickly move the flame over the cake until the meringue is just lightly browned, taking care not to burn. (The cake will last for 12 hours if it is not browned, for 2 days in the refrigerator if it is.)