Ingredients:

  • 4 tablespoons (56g) unsalted butter, melted and cooled slightly
  • 1/2 cup (100g) granulated sugar
  • 4 large eggs, separated (whites at room temperature)
  • 1/2 cup (60g) all-purpose flour, sifted
  • Zest from 2 medium lemons (about 1 tablespoon)
  • 2 tablespoons fresh lemon juice
  • 1 teaspoon vanilla extract
  • 2 cups (480ml) milk, warmed to lukewarm
  • Pinch of salt
  • 1-2 tablespoons powdered sugar, for dusting (optional)
  • Fresh lemon slices or zest curls, for garnish (optional)

Instructions:

  1. Preheat your oven to 325°F (160°C). Lightly grease and flour a 9x9 inch (23x23 cm) square baking pan, or line it with parchment paper leaving an overhang on two sides for easy removal. Set aside.
  2. Separate the eggs, placing the whites in a very clean, large mixing bowl and the yolks in another medium bowl. Add a pinch of salt to the egg whites and beat them with an electric mixer until stiff peaks form. Set aside at room temperature, ensuring they are ready to be gently folded into the batter later.
  3. In the bowl with the egg yolks, add the melted and slightly cooled unsalted butter and the granulated sugar. Beat with the electric mixer until the mixture is light, creamy, and well combined (the initial warmth of the butter helps this emulsion).
  4. Stir in the lemon zest, fresh lemon juice, and vanilla extract into the yolk mixture, mixing until just incorporated.
  5. Gradually add the sifted all-purpose flour to the yolk mixture, beating on low speed until just combined and no dry streaks remain. Avoid overmixing.
  6. Slowly pour the warmed milk (lukewarm temperature is critical for the emulsion stability and temperature differential) into the batter while whisking continuously until the mixture is smooth and completely incorporated. The batter will be very thin and liquidy at this stage.
  7. Gently fold the stiff egg whites into the liquid batter in three additions using a spatula. Do not overmix; the goal is to incorporate the whites without deflating them too much. The batter should still have some foamy bits on top, indicating the air needed for the sponge layer.
  8. Pour the prepared batter into the greased and floured (or parchment-lined) baking pan. Place the pan in the preheated oven and bake for 50-60 minutes, or until the top is golden brown and the cake is set but still slightly wobbly in the center. The low and slow heat allows the egg proteins to coagulate at different rates, forming the distinct layers.
  9. Remove the cake from the oven and let it cool completely in the pan on a wire rack. Once cooled, cover the pan and refrigerate for at least 2-3 hours, or preferably overnight, to allow the layers to fully set and the custard to firm up.
  10. Once chilled, carefully remove the cake from the pan. Dust with powdered sugar and garnish with fresh lemon slices or zest curls before serving.