Preheat the oven to 325°F. Line an 8×8-inch baking dish with parchment paper, leaving an overhang on the sides, and lightly grease with cooking spray. Set aside.

Whip the egg whites until stiff peaks form, then set aside.

In a separate bowl, beat the egg yolks and sugar until pale yellow.

Add the melted butter and vanilla extract, mixing until evenly combined.

Gradually mix in the flour until fully incorporated.

Stir in the lemon juice and lemon zest until well combined.

Slowly beat in the lukewarm milk until the mixture is smooth.

Gently whisk in the egg whites by hand, leaving small lumps. These lumps will float to the surface during baking, creating the cake’s top layer. Note: The batter will be very thin.

Pour the batter into the prepared pan and bake for 40-60 minutes, until the center is slightly jiggly but the top is firm to the touch. Baking time may vary depending on your oven or pan, so start checking after 35 minutes. If the top browns too quickly, cover it with aluminum foil. Avoid overbaking, as this will result in a rubbery texture instead of a custardy center.

Let the cake cool completely before dusting with powdered sugar.

Store any leftovers in the refrigerator.