Passover Chocolate Mousse Cake

Grease 17- x 11-inch (45 x 29 cm) rimmed baking sheet; line with parchment paper. Set aside.

Sponge Cake: In large bowl, beat eggs with sugar until pale and thick enough that batter falls in ribbons when beaters are lifted, about 5 minutes. Sift potato flour and cocoa over top; fold in. Spread in prepared pan. Bake in centre of 350°F (180°C) oven until cake springs back when lightly touched, about 12 minutes. Let cool in pan on rack. With serrated knife, trim about 1/4-inch (5 mm) from edges of cake to cut off crusty edges. Cut cake crosswise into 4 equal rectangles; set aside.

Chocolate Mousse: In bowl over saucepan of hot (not boiling) water, melt chocolate, stirring often. Remove from heat; set aside. In separate bowl, beat whip topping until soft peaks form; set aside.

In third bowl, whisk egg yolks with sugar; place over saucepan of simmering water and cook, whisking constantly, for 2 minutes. Reduce heat to low. Whisk in half of the chocolate; whisk in remaining chocolate. Whisk in one-third of the whipped topping. Remove from heat. Fold in remaining topping. Refrigerate until firm but still spreadable, 10 to 15 minutes.

Remove 2 cups (500 mL) of the mousse; set aside. Place 1 piece of cake on rectangular cake plate. Spread with one-third of the remaining mousse. Repeat layers twice; top with remaining cake. Spread 1-1/2 cups (375 mL) of the reserved mousse over top and sides. Using piping bag, pipe remaining mousse into rosettes on top edges.

Refrigerate for at least 1 hour or for up to 24 hours. Garnish with fruit.

Additional information :

Substitution: For a non-Passover version, use sifted cake-and-pastry flour instead of the potato flour, and whipping cream instead of the whip topping.