MOCHA LAYER CAKE WITH CHOCOLATE-RUM CREAM FILLING

INGREDIENTS:

Filling and Topping:
4 cups whipping cream
1/4 cup (1/2 stick) unsalted butter
1/4 cup sugar
20 ounces semisweet chocolate, finely chopped; plus 2 ounces, chopped separately
1/3 cup dark rum
2 teaspoons vanilla extract

Syrup:
1/4 cup water
2 tablespoons sugar
2 tablespoons dark rum

Cake:
1 1/2 teaspoons vanilla extract
3/4 teaspoon instant coffee powder
2/3 cup cake flour
3 tablespoons unsweetened cocoa powder
1/2 teaspoon baking soda
3 large eggs, separated
3/4 cup sugar
1/4 teaspoon cream of tartar
1/4 teaspoon salt

DIRECTIONS:

For filling and topping:
Stir first 3 ingredients in heavy large saucepan over medium-high heat until sugar dissolves and cream comes to simmer. Remove from heat. Add 20 ounces chocolate; whisk until melted and smooth. Whisk in rum and vanilla. Transfer 1 cup warm chocolate mixture to small bowl; whisk remaining 2 ounces chocolate into mixture in bowl and set aside for topping. Cover; let stand at room temperature. Transfer remaining chocolate mixture to large bowl to use as filling; chill until cold and thick, at least 6 hours and up to 1 day.

For syrup:
Stir water and sugar in small saucepan over low heat just until sugar dissolves. Remove from heat; mix in rum. Cover and let stand up to 1 day.

For cake:
Preheat oven to 350°F. Butter 9x9x2-inch metal baking pan. Line bottom with waxed paper; butter paper. Combine vanilla and coffee powder in cup; swirl to dissolve coffee. Sift flour, cocoa, and baking soda into small bowl. Using electric mixer, beat egg yolks and 1/2 cup sugar in medium bowl until very thick and light in color, about 3 minutes. Beat in vanilla-coffee mixture. Using clean dry beaters, beat egg whites, cream of tartar, and salt in large bowl until soft peaks form. Gradually add remaining 1/4 cup sugar, beating until stiff but not dry. Fold 1/3 of whites into yolk mixture. Fold in half of flour mixture. Fold in half of remaining whites, then remaining flour mixture, then remaining whites. Transfer batter to prepared pan; gently spread to even thickness …