Heat oven to 375°F. Grease 15x10x1-inch baking pan. Line with waxed paper; grease paper. Set aside.
Beat egg whites in bowl at high speed until foamy. Continue beating, gradually adding 1/4 cup sugar, until glossy and stiff peaks form.
Combine remaining 1/2 cup sugar, egg yolks, 3 tablespoons water and 1/2 teaspoon vanilla in bowl. Beat at high speed, scraping bowl often, 5-6 minutes or until thick and lemon-colored. Gently stir in flour and baking powder. Gently stir egg yolk mixture into beaten egg whites.
Pour batter into prepared pan. Bake 14-18 minutes or until top springs back when touched lightly in center. Cool 10 minutes; remove from pan. Cool completely.
Combine 1/2 cup sugar, 1/2 cup water and espresso powder in 1-quart saucepan. Cook over medium heat 3-4 minutes or until mixture comes to a full boil. Boil 1 minute; stir in rum. Cool completely.
Cut cake crosswise into three (10x5-inch) pieces. Brush top of each piece generously with syrup mixture, reserving 2 tablespoons syrup mixture.
Place 1 piece cake, syrup-side up, on serving plate. Stir together powdered sugar, mascarpone cheese and vanilla in medium bowl. Stir in 2 ounces grated chocolate. Spread half of filling on top of cake on serving plate. Repeat layering; top with third cake layer.
Beat whipping cream in bowl at high speed, scraping bowl often, until soft peaks form. Continue beating, gradually adding 2 tablespoons syrup mixture, until stiff peaks form. Spread 1 cup whipped cream on top of cake; sprinkle with remaining grated chocolate. Pipe or spread remaining whipped cream on sides of cake. Refrigerate at least 3 hours.
Cut torte into 8 slices; cut each slice in half. Store refrigerated.
*Substitute 1 teaspoon rum extract.
**Substitute 2 (8-ounce) packages cream cheese, softened.