Preheat the oven to 350°F (175°C). Grease and lightly flour a 9×13-inch baking dish.
In a medium bowl, sift together the flour, cocoa powder, baking powder, and salt.
In a large mixing bowl, beat the egg yolks with 3/4 cup of granulated sugar until pale and fluffy. Stir in the whole milk and vanilla extract.
Gradually mix the dry ingredients into the egg yolk mixture until just combined.
In a separate clean bowl, beat the egg whites until soft peaks form. Gradually add the remaining 1/4 cup of sugar and continue beating until stiff peaks form.
Gently fold the beaten egg whites into the batter until no white streaks remain.
Pour the batter into the prepared baking dish and bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool for 10 minutes. Use a fork or skewer to poke holes all over the surface of the cake.
In a medium bowl, whisk together the sweetened condensed milk, evaporated milk, whole milk, and chocolate syrup until smooth.
Slowly pour the milk mixture over the cake, ensuring it seeps into the holes. Cover and refrigerate for at least 4 hours or overnight.
In a large bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract until stiff peaks form.
Spread the whipped cream over the chilled cake. Garnish with chocolate shavings or a dusting of cocoa powder if desired.
Slice and serve chilled. Enjoy!