Preheat oven to 350 degrees F.
In a medium size bowl combine the flour, cocoa powder, baking powder and salt. Stir together with a fork.
Separate the eggs, whites in a medium size mixing bowl and yolks in a large mixing bowl. Combine the egg yolks with 3/4 cup of sugar, stir together until fluffy.
Add in the vanilla extract. Stir to combine.
Add the dry ingredients to the wet ingredients, stir to combine, will be dry
Add in the milk. Stir to mix.
Whisk the egg whites with a hand or stand mixer, once the egg whites start getting foamy and white in color add in the last 1/4 cup of sugar. Continue whisking or mixing on high speed until smooth, white, and stiff peaks form, approximately 10 minutes.
Fold the egg whites into the cake batter.
Grease a 9×13 cake pan. Pour the cake batter into the cake pan. Bake for 30 minutes or until a toothpick inserted in the center of the cake comes out clean.
In a large measuring cup combine the milks and cocoa powder needed for the milk mixture. Whisk together. (sift the cocoa powder to make this easier)
When the cake is cooled to room temperature. Poke all over the top with a fork. Then pour the milk mixture over the entire cake. (if there are lumps of cocoa powder in the milk mixture, you can pour the milks through a fine metal strainer as you pour over the cake).
Cover the cake and chill in the refrigerator for at least 4 hours to overnight.
After the cake has chilled and soaked in the milks, prepare the whipped cream. Add the heavy cream to a large mixing bowl. Mix on medium speed until cream starts to thicken, then add in the powdered sugar, cocoa powder and vanilla extract. Continue mixing on medium to high speed until soft peaks form.
Spoon the whipped cream onto the cake, spread with a spatula or butter knife.
Top with finely chopped chocolate.
Keep cake in the refrigerator until ready to serve. Store any leftovers in the refrigerator. Cake is best served cold.