Step 1: Prepare the Chocolate Sponge Cake

1. Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking pan.
2. In a bowl, whisk together flour, cocoa powder, baking powder, and salt.
3. In a separate bowl, beat egg yolks with ¾ cup sugar until light and creamy. Stir in milk and vanilla.
4. Slowly fold in the dry ingredients until just combined.
5. In another clean bowl, beat egg whites until soft peaks form. Gradually add the remaining ¼ cup sugar and beat until stiff peaks form.
6. Gently fold the whipped egg whites into the batter in three additions.
7. Pour into the prepared pan and bake for 35-40 minutes or until a toothpick inserted in the center comes out clean.
8. Let the cake cool for at least 20 minutes.

Step 2: Prepare the Chocolate Tres Leches Mixture

1. In a bowl, whisk together whole milk, evaporated milk, condensed milk, and cocoa powder.
2. Using a fork, poke holes all over the cake.
3. Slowly pour the chocolate milk mixture over the cake, ensuring even absorption.
4. Cover and refrigerate for at least 2 hours, preferably overnight.

Step 3: Make the Whipped Cream Topping

1. In a cold mixing bowl, beat heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
2. Spread evenly over the soaked cake.
3. Dust with cocoa powder and garnish with chocolate shavings.

Step 4: Serve & Enjoy

1. Serve chilled for the best texture and flavor.
2. Pair with fresh berries or a drizzle of dulce de leche for an extra treat.