Preheat the oven to 350°F.
In a medium bowl, whisk or sift together the flour, baking powder, espresso powder and salt. Set aside.
In a bowl of a stand mixer fitted with a whisk attachment, add the egg yolks along with ¾ cup of the sugar. Beat on high speed until the yolks are pale yellow, about 5 minutes. Slowly add the evaporated milk and vanilla extract and mix until combined. Add the flour mixture to the egg yolk mixture and stir gently just until just combined. Do not over-mix.
In another bowl, beat the egg whites on high speed. As they begin to whip into stiff peaks, gradually mix in the remaining ¼ cup sugar. Beat on high until stiff peaks form.
Using a rubber spatula, fold the beaten egg whites into the batter very gently, scraping the bottom and sides of the bowl, until combined. Pour the batter into an ungreased 9x13-inch baking pan and smooth into an even layer. Bake for 25 to 30 minutes or until a toothpick inserted in the center comes out clean.
Meanwhile, in a large measuring cup or bowl with a spout, whisk together the condensed milk, heavy cream, reserved evaporated milk, espresso and vanilla.
Once the cake is done, remove from the oven and allow it to rest for 5 minutes before pouring all of the soaking mixture over the cake. The cake must be warm at the time you add the soak so that it absorbs very well. Allow to cool completely while you prepare the topping.
For the topping, add the mascarpone, heavy cream, powdered sugar, and vanilla to a bowl of a stand mixer fitted with the whisk attachment. Beat on moderate speed until soft peaks form. Then raise the speed and beat on high until firm.
Pour onto the cooled cake and spread out into an even layer. Cover with plastic wrap and chill for at least 3 hours or overnight. Once ready to serve, dust the cake with cocoa powder to completely cover the top. Slice and serve immediately. Enjoy!