Instructions
Prepare the Pan: Preheat your oven to 325°F (160°C). Line an 8×8 inch square baking pan or loaf pan with parchment paper, leaving overhang on two sides for easy removal. Lightly grease the parchment with butter or cooking spray. The parchment is essential for this delicate cake, as it ensures clean removal after baking. This lower baking temperature is crucial for creating the distinct layers.
Separate and Prepare Eggs: Carefully separate the egg whites from the yolks, ensuring no yolk gets into the whites. Even a tiny bit of yolk will prevent the whites from whipping properly. Place the whites in a very clean, dry bowl and set aside at room temperature. Room temperature eggs separate more easily and whip better. Put the yolks in a large mixing bowl.
Beat Egg Yolks: Using an electric mixer, beat the egg yolks with half the sugar (about six tablespoons) and the tablespoon of water on medium-high speed for three to four minutes until the mixture is pale yellow, thick, and creamy. The mixture should form ribbons when you lift the beaters. This extended beating incorporates air and creates volume. Add the vanilla extract and melted butter, beating until well combined. The butter should be melted but not hot, or it will cook the eggs.
Add Flour: Sift the flour over the egg yolk mixture to avoid lumps. Using a whisk or spatula, gently fold the flour into the mixture until just combined. Don’t overmix. The batter will be quite thick at this point, which is exactly what you want.
Add Milk: This is the magic step. Gradually add the lukewarm milk to the batter while whisking constantly. Add it slowly, whisking thoroughly after each addition. The milk must be lukewarm, not cold or hot. Cold milk will cause the butter to solidify into lumps, while hot milk will cook the eggs. Add the lemon juice and continue whisking. The batter will become very thin and liquidy, almost like water. This is correct and essential for the magic layers to form. Don’t panic at the thin consistency; it’s supposed to be this way.
Whip Egg Whites: In a separate clean bowl with clean beaters, beat the egg whites with a pinch of salt on medium speed until foamy. Gradually add the remaining sugar (about six tablespoons) one tablespoon at a time while beating. Increase the speed to high and continue beating until stiff peaks form. The whites should be glossy and hold firm peaks when you lift the beaters. This usually takes four to five minutes. Properly beaten whites are crucial for the top layer.
Fold Gently: Here’s the critical part: using a spatula, gently fold the beaten egg whites into the thin batter in three additions. Don’t stir or mix vigorously. Use a gentle folding motion, scooping from the bottom and folding over the top. The mixture will look lumpy and separated with visible white streaks. This is absolutely normal and correct. If you overmix, the layers won’t form. The batter should remain quite liquid with floating clouds of egg white.
Bake: Pour the batter into the prepared pan. It will be very liquidy. Bake for fifty to sixty minutes, or until the top is golden brown and set, with a slight jiggle in the center. The cake should not be completely firm; a little wobble is perfect. Don’t open the oven door during baking, as temperature fluctuations can affect the layer formation. The edges will be more golden than the center.
Cool Completely: This is crucial: let the cake cool completely in the pan at room temperature for at least two hours, then refrigerate for a minimum of four hours, preferably overnight. The layers need this time to set properly. The cake will be very jiggly when first removed from the oven but will firm up as it cools. Rushing this step will result in a messy cake that doesn’t slice cleanly.
Serve: Once fully chilled, use the parchment overhang to lift the cake from the pan. Dust generously with powdered sugar. Cut into slices with a sharp knife, wiping it clean between cuts. You should see three distinct layers: a dense, slightly spongy bottom, a creamy custard middle, and a light cake-like top.
Tips for Success
Use lukewarm milk, not cold or hot. Don’t overmix when folding in egg whites. Let the cake cool and chill completely before cutting for clean slices and distinct layers.
Storage
Store covered in the refrigerator for up to three days. This cake is best served chilled.
