1. Preheat your oven to 160°C (325°F). Lightly grease a 9×13 inch baking pan with non-stick cooking spray and set it aside.

2. Carefully separate the egg whites from the yolks, ensuring no yolk gets into the whites. In a large, clean mixing bowl, beat the egg whites with an electric mixer on medium-high speed until soft peaks form. Gradually add half of the granulated sugar (100g), continuing to beat until stiff, glossy peaks form. Set aside.

3. In a separate medium bowl, whisk together the plain flour, baking powder, and salt until well combined. Set aside.

4. In another bowl, beat the egg yolks with the remaining 100g granulated sugar until the mixture is pale yellow and thick. Beat in the 1 teaspoon vanilla extract (for the cake) and 80g milk (for the cake batter) until just combined.

5. Gradually add the whisked dry ingredients to the egg yolk mixture, mixing on low speed or by hand with a spatula until just combined. Be careful not to overmix, as this can lead to a tough cake.

6. Gently fold the beaten egg whites into the cake batter in two additions using a spatula. Be delicate to maintain as much air as possible, which is crucial for a light and airy sponge.

7. Scrape the airy batter into the prepared 9×13 inch cake pan. Gently tap the pan on your kitchen counter a few times to release any large air bubbles. Bake for 30-35 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. Rotate the cake halfway through baking for even browning.

8. Remove the cake from the oven and allow it to cool in the pan on a wire rack for at least 30 minutes. This helps it set before adding the milk soak.

9. While the cake cools, combine the 395g sweetened condensed milk, 340g evaporated milk, and 120g additional milk in a medium bowl. Whisk until all three milks are thoroughly combined.

10. Once the cake has cooled slightly (it should still be a bit warm), use a fork or a wooden skewer to poke holes evenly all over the surface. Ensure the holes go deep enough to allow the milk mixture to penetrate the cake. Slowly and evenly pour the entire milk mixture over the poked cake. Be patient and allow the cake to absorb the liquids.

11. Tightly cover the cake with plastic wrap, ensuring a good seal. Refrigerate for a minimum of 4 hours, or preferably overnight. Chilling allows the cake to fully absorb the milks and become wonderfully moist and flavorful.

12. Just before serving, in a medium mixing bowl, beat the 480ml heavy cream, 200g granulated white sugar, and 1 tsp vanilla extract (for the topping) using an electric mixer until medium peaks form. The cream should be thick and spreadable but not overly stiff.

13. Evenly spread the freshly whipped cream over the chilled and soaked Tres Leches Cake. For a classic touch, sprinkle with a pinch of ground cinnamon or garnish with fresh berries like strawberries or raspberries. Slice and enjoy your homemade Authentic Tres Leches Cake!