Preheat the oven to 350 and grease a 9x13 baking pan.
In a bowl, beat butter for about thirty seconds and add sugar. Beat for about a minute, until light.
Add egg whites one at a time, beating after each addition. Add vanilla and mix until combined.
Sift flour, baking soda, salt and baking powder together.
Lower the mixer speed to low.
Alternating, add flour mixture and buttermilk in two parts, starting and ending with dry ingredients. Mix until just combined.
Transfer the batter into the baking sheet, spread evenly. Bake for 20-25 minutes, until the toothpick inserted in the center comes out clean.
Cool completely before frosting!
Mascarpone Cream:
(Use whisk attachment) Beat the cold heavy cream and 1 tbs of sugar in the cold bowl of an electric mixer, until soft peaks appear. Set aside.
Thoroughly clean and dry the mixer before starting on the rest of the cream. Use the whisk attachment.
Whip the egg yolks and 3 tbs of sugar thoroughly, on medium-high speed, for about 3 minutes, until light yellow, think and frothy.
Add the mascarpone cheese and amaretto liqueur, mix on low-medium speed.
Gently fold the whipped cream into the mascarpone cream.
Tiramisu Cake:
Poke holes all over the cake.
Sprinkle the coffee over the top of the cake. Try to do it evenly and not too much so that the whole cake doesn't get soaked (just the top). You can use a spray bottle if you have one that you use for food, or just your hands.