In the bowl of an electric mixer fitted with the beater attachment, beat egg whites with sugar until stiff. Add egg yolks and oil and mix until combined.

Meanwhile, grate the chocolate on the larger hole of a box grater over a large bowl.

Add the potato starch and mix with a spoon until evenly combined. Add chocolate and potato starch slowly to batter, folding in with a spatula until batter is smooth.

Pour mixture into a Gefen Parchment Paper-lined 9- x 13-inch pan or three 9-inch round pans. Bake for one hour for the 9- x 13-inch pan or 50 minutes for 9-inch rounds. Top with Hazelnut Cream (below).

Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Spread out nuts on a lined, rimmed baking sheet. Roast, shaking sheet once for even toasting, until deep brown, about 13–15 minutes.

Let cool completely. (If nuts have skins, rub them vigorously in a kitchen towel to remove.)

Grind hazelnuts and sugar in a food processor along with the oil until a fairly smooth,buttery paste forms, about one minute. Set aside.

Place chocolate in a medium-sized metal bowl. Set bowl over a pot of simmering water; stir until chocolate is melted and smooth.

Remove from heat; add butter or margarine,and whisk until completely incorporated. Whisk in remaining ingredients, including the hazelnut mixture.

Pour into clean glass jars, dividing equally. Let cool. (Paste will thicken and become soft and peanut-buttery as it cools.) Screw on lids. Use as spread for my Chocolate Fleck Cake, or as desired.