MOCHA LAYER CAKE WITH CHOCOLATE-RUM CREAM FILLING

Steps:

• 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.
• Bake cake until puffed and tester inserted into center comes out clean, about 18 minutes.
• Cool in pan on rack (cake may shrink slightly).
• Cut around pan to loosen cake.
• Turn out onto work surface; peel off paper.
• Using long serrated knife, cut cake horizontally in half.
• Place 1 half, cut side up, on platter.
• Drizzle half of syrup (about 3 1/2 Tablespoons) over cake.
• Using electric mixer, beat cold chocolate filling until thick and lighter in color, less than 1 minute.
• Spread all of filling evenly over cake layer, aligning with sides of cake (filling will be about 1 inch thick).
• Drizzle remaining syrup over cut side of second cake layer.
• Place second layer, syrup side down, atop filling; press to adhere.
• Rewarm topping over low heat just until pourable.
• Pour topping onto top center of cake.
• Using small spatula, spread topping to edges, being careful to keep it from spilling over.
• Chill cake up to 1 day, covering loosely with foil or with cake dome after 2 hours of chilling.
• Cut cake into 16 squares and serve.