chocolate curlsmade from grating a bar of chocolate, for garnish
Heat oven to 325 degrees and coat a 9X13-inch pan with cooking spray.
In a bowl, whisk together flour, cocoa powder, baking powder, and salt until there are no lumps.
Use a stand mixer with a whisk attachment to beat the egg whites until soft peaks form (if you lift the whisk attachment up, the eggs are just starting to have enough form to stay attached to the whisk.)
With mixer on medium, gradually add the 1 1/2 cups sugar. Increase to high and beat until stiff peaks form (egg whites completely hold their shape even if you move the whisk attachment around.)
Whisk in the egg yolks.
Whisk in milk and vanilla extract.
Remove bowl from mixer and use a rubber spatula to gently fold the flour mixture in until no pockets of flour remain.
Pour batter into prepared pan and bake for 30 to 35 minutes. Cool completely.
In a bowl, whisk together 1 cup heavy cream, sweetened condensed milk, evaporated milk, and coffee. Slowly pour over cooled cake. Most of it with sink down around the edges and it will look like there is way too much liquid, but it will all get absorbed. Cover with plastic wrap (Try not to let the plastic touch the cake) and refrigerate at least 2 hours (can be done a day in advance).
To make whipped topping, use electric mixer to beat heavy cream. Once it starts to thicken, add confectioners' sugar, vanilla, and Kahlua. Beat until cream gets thick. Spread on top of cake.