1lbmascarpone(I suggest making your own if you have time--it's much better and cheaper)
To make the cake
Preheat the oven to 375 F. Line two 9" cake pans with parchment paper, but do not grease them in any way.
Whip the egg yolks with half of the sugar (3 oz, or 7 tbsp) in the bowl of a large stand mixer on high speed for 5 minutes, until they are very thick and light in color. Transfer the yolks to a separate bowl and wash the mixing bowl and whisk very well.
Whip the egg whites in the cleaned mixing bowl until soft peaks form. Gradually add the remaining 3 oz/7 tbsp sugar a spoonful at a time, while mixing on high speed, until the egg whites hold firm peaks.
Fold one-third of the egg whites into the yolks with a spatula, then sift half of the cake flour on top and gently fold it in. Fold a second third of the egg whites into the yolks, sift the remaining cake flour on top, then fold that in. Finally, add the last of the egg whites, and when they're almost incorporated, add the lemon zest and fold until everything is mixed together.
Divide the batter between the two pans and bake for 18-22 minutes, until the tops are golden, firm, and a toothpick inserted in the center comes out clean. Transfer the cakes to a rack to cool completely.
To make the lemon syrup
Heat the sugar and water in a small saucepan over medium-high heat, stirring occasionally, until the sugar dissolves and the liquid is clear. Remove from the heat and stir in the lemon juice. Allow to cool completely before use.
To make the lemon curd
Fill the bottom of a double-boiler with 2 inches of water and bring it to a simmer.
Place the eggs, yolks, and sugar in the top of the double boiler (off the heat) and whisk until blended. Add the lemon juice and mix well. j
Place the egg mixture over the simmering water and cook, whisking constantly, until the curd reaches 180 F on a candy thermometer. (If you don't have a thermometer, it should thicken enough to coat the back of a spoon.) Don't let the curd boil, or you'll have bits of scrambled egg in your curd.
Once cooked, strain the curd through a metal strainer into a bowl. Add the cold butter pieces to the curd, and whisk gently until the butter melts and the mixture is velvety-smooth. Press a layer of cling wrap on top of the curd and refrigerate it until it is cool, at least 3-4 hours or overnight.
To make the mascarpone filling
Place the cream and sugar in the large bowl of a stand mixer and whisk until they form firm peaks, but do not over-beat or it will become grainy and curdled.
In a large bowl, combine the mascarpone and 1-1/2 cups of lemon curd, and stir until they're well-mixed. It should be the consistency of pudding. Gently fold the whipped cream into the mascarpone mixture, being careful not to overmix, or the mascarpone will look grainy and separated. If this happens, stir in a spoonful or two of heavy cream to smooth it out.
To assemble the cake
Unmold the cakes, and use a sharp serrated knife to cut each one in half, so you're left with four thin cake rounds. Place one round on a cake cardboard and brush it with a quarter of the lemon syrup.
Spoon about 1/3 cup of the mascarpone filling on top of the cake round, and use a spatula to spread it evenly around. Top the mascarpone with about 1/3 cup of lemon curd, and spread it in a thin layer.
Place another cake round on top of the first, and brush this one with an equal amount of lemon syrup. Repeat the layer of cake rounds, lemon syrup, mascarpone, and lemon curd until you have added the final cake round to the top of the cake. Brush the top with the remaining lemon syrup.
Spread the remaining mascarpone mixture along the top and sides of the cake. If you have lemon curd left over, you can pipe dots of lemon curd along the top of bottom border of the cake (or you can just save it to eat on toast and oatmeal!)
This cake is best made a few hours--or even a day or two--in advance, so the flavors and textures have a chance to meld.
adapted from The Art and Soul of Baking by Cindy Mushet