Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Beat egg whites until stiff. Set aside.

In a separate bowl, beat the yolks with the sugar until lemony and thick. Add the oil, cocoa, coffee, salt, and vanilla sugar. Mix well. Put the potato starch into a small sifter (see note) and, while mixing at a low speed, gently sift it over the batter in the mixer. Mix just until the potato starch is incorporated, make sure not to over-mix.

Gently fold in beaten whites. Pour batter into a greased tube pan and bake for approximately 45 minutes, or until the cake is done. Take care not to burn the cake. If the top begins to burn (since this cake rises high, the top can get scorched), cover loosely with foil and continue baking until the inside is ready.

Alternate method: Instead of baking the cake in the oven (not everybody has a Pesach oven!), pour the mixture into a well-greased wonder pot and bake it on top of the stove for 45 minutes, or until done. Make sure the flame is low and that the wonder pot is centered on the fire — and don’t take any sneak peeks during cooking! Pesach cakes are very fragile and are full of a lot of air. That’s why they plop if not “treated” properly.