Tunnel Of Chocolate Mousse Cake 

1 cup egg whites
1/2 cup unsweetened cocoa
3/4 cup boiling water
1 3/4 cup cake flour
1 3/4 cups sugar
1 1/2 tsp. soda
1 tsp. salt
1/2 cup salad oil
7 egg yolks
2 tsp. vanilla
1/2 tsp. cream of tartar 

Filling:

3 cups heavy cream
1 1/2 cups powdered sugar
3/4 cups cocoa
2 tsp. vanilla
1/4 tsp. salt
1 tsp. unflavored gelatin 

In large mixing bowl, let whites warm to room temperature for 1 hour. Into cocoa in small bowl, stir boiling water, stirring until smooth. Let cool. Preheat oven to 325 F.  Sift flour with sugar, soda and salt in large bowl. Make well in center. Pour in oil, vanilla and cocoa. With wooden spoon, beat just until smooth. Sprinkle cream of tartar over egg whites. Mix at high speed until very stiff peaks form. Do not underbeat. Pour batter over whites. With over and under motion, gently fold to combine. Turn into 10 inch ungreased tube pan. Bake 60 to 65 minutes, until op springs back when pressed with finger. Invert over neck of bottle; cool 1 ½ hours. With spatula, loosen cake, remove and cool on rack.  Make filling. In large bowl combine cream, sugar, cocoa, vanilla, salt. Refrigerate for 1 hour. With mixer beat until stiff; refrigerate. Sprinkle gelatin over 2 tbsp. Cold water to soften. Heat, stirring, over hot water to dissolve, then cool. Prepare cake. Cut a 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 chilled gelatin. Use to fill cavity. Replace top. Mix 1/2 cup filling with reserved crumbled cake. Use to fill center hole. Frost top and sides of cake with remaining filling. Refrigerate until serving.