Recipe(tried): McCall's Cooking School Chocolate Chiffon Mousse Cake (with chocolate mousse tunnel)

CHOCOLATE CHIFFON CAKE
Source: McCall's Cooking School
Makes 1 (10-inch) tube cake; 12 servings

1 cup egg whites (7 or 8)
1/2 cup sifted unsweetened cocoa
3/4 cup boiling water
1 3/4 cup sifted cake flour
1 3/4 cup sugar
1 1/2 teaspoons baking soda
1 teaspoon salt
1/2 cup salad oil
7 egg yolks
2 teaspoons vanilla extract
1/2 teaspoon cream of tartar
CHOCOLATE FILLING:
3 cups heavy cream
1 1/2 cups sifted confectioner's sugar
3/4 cup sifted unsweetened cocoa
2 teaspoons vanilla extract
1/4 teaspoon salt
1 teaspoon unflavored gelatine

NOTE: All sifted ingredients should be sifted BEFORE measuring!

MAKE CAKE:
In large electric mixer bowl, let whites warm to room temperature (about 1 hour).

Into cocoa in small bowl, stir boiling water until smooth. Let cool 1/2 hour.

Preheat oven to 325 degrees F.

Sift flour with sugar, soda and salt in large bowl. Make a well in center. Pour in oil, yolks, vanilla and cocoa. With wooden spoon, beat just until smooth.

Sprinkle cream of tartar over egg whites. With mixer at high speed, beat until very stiff peaks form when beater is slowly raised. Do not under beat. Pour batter over whites. With whisk, and an under-and-over motion, gently fold to combine. Turn into ungreased 10-inch tube pan.

Bake 60-65 minutes, until top springs back when pressed with finger. Invert over neck of bottle. Cool 1 1/2 hours.

With spatula, loosen cake and remove. Cool on rack.

MAKE CHOCOLATE FILLING:
In large bowl, combine cream, sugar, cocoa, vanilla, salt & refrigerate for 1 hour.

With mixer, beat until stiff, refrigerate again.

Sprinkle gelatine over 2 tablespoons cold water to soften. Heat, stirring over hot water to dissolve (double boiler effect). Cool; set aside.

ASSEMBLE CAKE:
Cut 1-inch slice crosswise from top of cake, set aside. With sharp knife, outline a cavity in cake, leaving 1-inch thick walls around center, side and bottom. With spoon carefully remove cake from this area. Reserve 1 1/2 cups crumbled cake.

Measure 2 1/2 cups chocolate filling into small bowl. Fold in gelatine. Use to fill cavity. Replace top.

Mix 1/2 cup filling with reserved crumbled cake. Use to fill center hole.

Frost top and side of cake with remaining filling. Refrigerate until serving.