1. Prepare CHOCOLATE MOUSSE FILLING. Chill 6 to 8 hours or overnight.
2. Prepare cake.* Heat oven to 375°F. Line 15-1/2x10-1/2x1-inch jelly-roll pan with foil; generously grease foil. Sprinkle linen or thin cotton towel with 1/4 cup powdered sugar.
3. Beat egg whites in large bowl until soft peaks form; gradually add 1/2 cup granulated sugar, beating until stiff peaks form. Beat egg yolks and vanilla in medium bowl on medium speed of mixer 3 minutes. Gradually add remaining 1/3 cup granulated sugar; continue beating 2 additional minutes.
4. Stir together flour, cocoa, baking powder, baking soda and salt; add to egg yolk mixture alternately with water, beating on low speed just until batter is smooth. Gradually fold chocolate mixture into beaten egg whites until well blended. Spread batter evenly in prepared pan.
5. Bake 12 to 15 minutes or until top springs back when touched lightly in center. Immediately loosen cake from edges of pan; invert onto prepared towel. Carefully peel off foil. Immediately roll cake and towel together starting from narrow end; place on wire rack to cool completely.
6. Carefully unroll cake; remove towel. Gently stir filling until of spreading consistency. Spread cake with filling; reroll cake. Refrigerate several hours. Sift powdered sugar over top just before serving. Serve drizzled with syrup and garnished as desired. Cover; refrigerate leftover cake roll. 8 to 10 servings.
CHOCOLATE MOUSSE FILLING
1/4 cup sugar
1 teaspoon unflavored gelatin
1/2 cup milk
1 cup HERSHEY'S SPECIAL DARK Chocolate Chips or HERSHEY'S Semi-Sweet Chocolate Chips
2 teaspoons vanilla extract
1 cup (1/2 pt.) cold whipping cream
1. Stir together sugar and gelatin in small saucepan; stir in milk. Let stand 2 minutes to soften gelatin. Cook over medium heat, stirring constantly, until mixture just begins to boil.
2. Remove from heat. Immediately add chocolate chips; stir until melted. Stir in vanilla; cool to room temperature.
3. Beat whipping cream in small bowl until stiff. Gradually add chocolate mixture, folding gently just until blended. Cover; refrigerate until ready to use. About 3 cups filling.
* Cake may be prepared up to two days in advance. Keep cake rolled tightly and covered well so that it doesn't get dry.