Mocha Layer Cake with Chocolate-Rum Cream Filling

INGREDIENTS

• 3 large eggs, separated
• 3 tablespoons unsweetened cocoa powder
• 4 cups whipping cream
• 1/3 cup dark rum
• 1/4 teaspoon salt
• 1/4 cup water
• 1 1/2 teaspoons vanilla extract
• 1/2 teaspoon baking soda
• 20 ounces semisweet chocolate, finely chopped; plus 2 ounces, chopped separately
• 1/4 teaspoon cream of tartar
• 2 tablespoons dark rum
• 1/4 cup sugar
• 2 tablespoons sugar
• 2/3 cup cake flour
• 3/4 cup sugar
• 1/4 cup (1/2 stick) unsalted butter
• 3/4 teaspoon instant coffee powder
• 2 teaspoons vanilla extract