This is a crustless, light verison of an Italian cheesecake. I find that baking it a day in advance and refrigerating it is not only convenient, but it also makes cutting a bit easier. Ricotta cake goes beautifully with an kind of berry.
*It is best to separate the eggs straight from the refrigerator, while they are still cold, as the egg yolks tends to break up as they warm. Make sure the whites have come to room temperature before beating.
Before using the ricotta, it is important to get it as dry as possible. To do this, place the ricotta in a fine-mesh sieve set over a bowl. Cover with cling wrap and set a heavy can on top to weigh it down. (This helps the draining process.) Refrigerate for several hours.
Preheat the oven to 350 degrees. Grease a 9-by-2-inch springfoam pan with the butter and dust it with 1 tablespoon of the flour. Invert the pan and tap to shake out excess flour.
In a large bowl, combine the ricotta, the remaining 2 tablespoons flour, the egg yolks, lemon zest, and pine nuts.
Place the egg whites in the bowl of an electric stand mixer. Using the balloon whisk attachment, beat the whites at high speed until soft, stiff peaks form.
Gradually beat in the sugar until the whites are stiff.
With a rubber spatula, fold ½ the whites into the ricotta mixture. Reverse the process and pour the ricotta mixture into the bowl with the remaining whites. Gently blend the ingredients, making a motion like a figure-8 with the spatula, until the egg whites are well combined.
Spoon the butter into the prepared pan and smooth the top. Place the pan on a sheet of aluminum foil on the middle shelf of the oven (in case the batter drips). Bake until the middle of the cake is firm to the touch and the top is golden, about 40 to 45 minutes.
Cool on a wire rack. The cake will fall a bit. Release the side of the pan, loosen the cake around the edges with a metal spatula, and remove the rim. Cover the cake with cling wrap and refrigerate.