Preheat the oven to 350°F (175°C). Lightly grease the bottom of a 12×7.5-inch enameled or metal baking dish. Do not grease the sides.
Whip the egg whites in a stand mixer on medium-high speed (speed four on KitchenAid stand mixer) for 2–3 minutes. Gradually add sugar, one tablespoon at a time, and continue mixing until medium peaks form.
Remove the mixer bowl and gently fold in the egg yolks using a whisk until no yellow streaks remain.
Add griz (semolina) 2–3 tablespoons at a time, folding gently after each addition to keep the batter airy and well incorporated.
Pour the batter into the prepared baking dish and smooth the top with a spatula. Bake for 30 minutes, or until the top is lightly golden. The cake will puff up while baking and settle slightly as it cools.
While the cake bakes, heat 5 cups of milk in a saucepan. Add 2 tablespoons of sugar and 1 packet of vanilla sugar. Bring to a light boil, then immediately turn off the heat.
After turning off the heat, stir the milk occasionally to prevent a skin from forming as it cools slightly.
When ready to soak the cake, pour the hot milk slowly over the entire surface of the cake through a fine mesh strainer to catch any milk skin. Make sure to reach the edges. Optionally, poke a few small holes with a skewer for better absorption.
Let the cake sit at room temperature for 2 hours, then cover the dish with plastic wrap. Transfer it to the refrigerator and chill for at least 6 hours or overnight before serving.
Notes
Only grease the bottom of the pan, not the sides. This helps the sponge rise evenly and prevents the center from collapsing.
Whip egg whites to medium peaks, then gently fold in the yolks and griz (semolina) to preserve the airy structure.
Use a smaller baking dish (around 12×7.5") for a taller sponge and better milk absorption.
Pour hot milk over hot cake for best absorption. Slowly pour the sweetened milk over the entire surface, ensuring it reaches the edges.
Strain the milk before (or while) pouring to remove any skin or solids, keeping the surface silky and smooth.
Let the cake cool at room temperature for about 2 hours, then cover it with plastic wrap and refrigerate for at least 6 hours, or overnight, for the best texture and flavor.