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1
Preheat oven to 325 degrees F (165 degrees C).
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2
Spray a 10-inch tube pan with cooking spray.
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3
Sift matzo cake meal with potato starch into a bowl; set aside.
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4
Place egg yolks into a large mixing bowl and beat with an electric mixer on medium speed until light, about 3 minutes.
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5
Slowly beat 1 cup sugar into the egg yolks; continue beating until mixture is thick and pale, about 5 more minutes. Beat cocoa powder into the egg yolk mixture until thoroughly combined.
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6
Beat egg whites with an electric mixer fitted with clean beaters in a separate bowl until foamy. Gradually beat in 1/2 cup sugar and continue to beat until egg whites hold stiff peaks.
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7
Lightly stir matzo cake meal mixture and coffee into egg yolk-cocoa mixture.
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8
Gently fold 1/3 of the egg whites into the batter, retaining as much volume as possible. Fold in remaining egg whites, mixing just until no white streaks remain. Gently mix in chopped walnuts.
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9
Spoon the batter evenly into the prepared tube pan.
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10
Bake in the preheated oven until top of cake shows small cracks and springs back when lightly pressed, about 45 minutes.
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11
Run a knife around the sides of cake to loosen from the pan. Invert cake onto a wire rack to cool.
