Heat oven to 350°F.
Grease 15 x 10 x 1-inch baking pan, or coat with cooking spray. Line bottom of pan with waxed paper; grease paper, or coat with spray.
Sift flour, cocoa powder and 1/8 teaspoon salt onto a second sheet of waxed paper.
Beat egg whites, cream of tartar and remaining 1/8 teaspoon salt in large bowl at high speed until frothy. Beat in sugar, 1 tablespoon at a time, until soft peaks form. On low speed, beat in egg yolks and vanilla just until blended. Gently fold flour mixture into egg white mixture. Spread evenly in prepared pan.
Bake in 350°F oven for 18 minutes or until cake springs back when lightly touched with fingertip. Cool cake in pan on wire rack 10 minutes. Invert pan onto wire rack; remove pan and waxed paper. Cool the cake completely.
Cut cake lengthwise into 3 equal strips.
Cut single cardboard strip the exact size of 1 cake strip; wrap in aluminum foil. Place 1 cake strip on top of cardboard.
Cut ice-cream brick lengthwise into 4 equal pieces. Place 2 ice-cream pieces on cake on cardboard, ends of ice cream flush with ends of cake. Fill in gap in center with ice-cream scraps. Repeat layering with cake and ice cream, ending with cake strip on top. Freeze several hours or until cake is firm. (Cake can be frozen tightly wrapped for up to 1 month.)
Stir together chocolate, 1/4 cup heavy cream and coffee in small, heavy saucepan. Heat over low heat, stirring, until mixture is smooth and chocolate is melted. Spread mixture over top of cake.
Beat remaining 1-3/4 cups heavy cream in small bowl until soft peaks form. Spread evenly over sides of cake. Serve immediately.