The Method

• Preheat your oven to 325°F. Assemble a well-buttered springform pan atop a sheet of aluminum foil and tightly gather that foil around the springform. NOTE: use the single tablespoon of VERY COLD butter to "seal the seam" all the way around, pressing the butter into the seam like caulk. Place into a refrigerator until ready to assemble. Set all atop a baking sheet. Alternatively, butter a 9-inch x 9-inch baking dish, lining the bottom and sides with parchment paper. Leave a 2-inch overhang on the parchment. Set aside.
• Pour the milk into a saucepan and set it over medium low heat. Stir occasionally.
• Prepare the apples by peeling, coring, and chopping into 1/2-inch pieces. Toss in a bowl with the juice of the half lemon. Apple pieces should be coated with the juice, but LIGHTLY. You want just enough acid to keep the apple from browning, but not too much that the batter won't set properly.
• Arrange the apple pieces in the bottom of the springform pan (or 9 x 9-inch baking dish). They may be loose, but they must fall beneath the inside middle of the pan if you were to imagine a line going all the way around.
• Separate the eggs using your fingers by allowing the whites to run through. Place the yolks remaining in your hand in a large mixing bowl. Beat the egg yolks with the granulated sugar until light and fluffy. The mixture will be very light in color and should be almost double in size. Add butter and vanilla extract and continue beating for another minute.
• After measuring and leveling your flour, hold a sifter or fine mesh sieve over the egg and sugar mixture and sift the flour into the mixture. Mix until fully incorporated. Slowly add the warmed milk. Beat until everything is well incorporated.
• In a clean bowl using clean beaters, beat the egg whites until stiff peaks form.
• Add the egg whites to the cake batter 1/3 at a time and gently fold them in. Do not fold the egg whites in completely. A few white streaks or lumps of egg white are encouraged.
• Pour batter into the prepared pan. Smooth out the top making sure batter seeps in between the apple pieces. Bake for 50 minutes or until the top is lightly golden. Baking times may vary. Begin testing for doneness at 50 minutes. The top will be slightly hard, nicely golden brown, and will not "jiggle" when you gently shake the springform. If the top appears golden but the cake is not yet set, cover loosely with foil and return to the oven, 10 minutes at a time, until it no longer jiggles.
• Cool the cake in the pan. For a springform, gently loosen the clasp to create a gap between the finished cake and the inside wall of the pan. If necessary, run the back of a knife all the way around. Keep the pan intact and cool the cake for at least 2 hours before cutting. For a 9 x 9-inch baking dish, use the parchment overhang to 'lift' the cooled cake from the dish. If necessary, run the back of a knife all the way around to loosen. Cool the cake the remainder of the way for at least 2 hours before cutting. NOTE: Slicing before the cake has fully cooled will result in the cake collapsing.
• To serve, remove the sides of the springform and place the bottom of the springform with the cake on a cake plate. Dust generously with Confectioner's sugar. Slice the cake and plate. Dust again with more Confectioner's sugar.