Preheat the oven to 350 degrees F. Lightly brush two 9-inch-round cake pans with vegetable oil. Line the bottom of the pans with parchment paper, then lightly oil the paper. Combine 2 tablespoons each potato starch and cocoa powder in a small bowl. Dust the prepared pans with the potato starch mixture, tapping out the excess.
Sift the matzo cake meal and the remaining 1/2 cup potato starch and 2/3 cup cocoa powder into a bowl. Put the eggs, granulated sugar and salt in a stand mixer bowl. Set the bowl over a saucepan of simmering water (do not let the bowl touch the water) and whisk until the sugar is dissolved and the mixture is hot (110 degrees F to 120 degrees F), about 5 minutes.
Attach the bowl to the stand mixer base and beat with the whisk attachment on high speed until very light and foamy, about 5 minutes. Whisk 1/3 cup vegetable oil, the food coloring and vanilla in a small bowl. Reduce the mixer speed to low; gradually beat the cocoa mixture into the egg mixture, then gradually beat in the oil mixture until just incorporated. Turn off the mixer and finish folding the batter with a rubber spatula until combined.
Divide the batter between the prepared pans, smoothing the tops. Bake until the cakes pull away from the pans and the centers spring back when pressed, about 30 minutes. Transfer to a rack and cool 15 minutes in the pans, then run a knife around the edges to loosen. Invert the cakes onto a parchment-lined baking sheet and let cool completely; peel off the parchment.
Make the frosting: Beat the cream cheese and butter in a large bowl with a mixer on high speed until smooth, about 1 minute. Reduce the speed to low and gradually beat in the confectioners' sugar, then the vanilla. Increase the speed to high and beat until smooth and fluffy, about 3 more minutes.
Transfer 1 cake layer to a platter and spread with 1 1/2 cups frosting; top with the second cake layer. Cover the whole cake with a very thin layer of frosting (this is the crumb coat; it doesn't have to be perfect). Refrigerate until firm, at least 30 minutes. Frost the top and sides of the cake with the remaining frosting, then return to the refrigerator until set, 1 to 2 hours.
Photograph by Con Poulos
For the best texture, be sure to use matzo cake meal (not matzo meal) and kosher potato starch.
Recipe courtesy Food Network Magazine