Step 1
Preheat oven to 325 degrees F (165 degrees C).
Step 2
Spray a 10-inch tube pan with cooking spray.
Step 3
Sift matzo cake meal with potato starch into a bowl; set aside.
Step 4
Place egg yolks into a large mixing bowl and beat with an electric mixer on medium speed until light about 3 minutes.
Step 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.
Step 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.
Step 7
Lightly stir matzo cake meal mixture and coffee into egg yolk-cocoa mixture.
Step 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.
Step 9
Spoon the batter evenly into the prepared tube pan.
Step 9
Bake in the preheated oven until top of cake shows small cracks and springs back when lightly pressed about 45 minutes.