Triple Chocolate Mousse Cake Ingredients Bottom Layer 6 tablespoons (3 oz) unsalted butter, cut into 6 pieces 7 oz bittersweet chocolate, finely chopped 3/4 teaspoon instant espresso powder 4 large eggs, at room temperature and separated 1 1/2 teaspoons vanilla extract pinch salt 1/3 cup packed light brown sugar (2 1/2 oz) Middle Layer