Viennese Dobos Torte

Name: Viennese Dobos Torte
Ingredients: 10 large eggs, separated, at room temperature; 1 cup granulated sugar; 2 1/2 sticks (10 ounces) unsalted butter, softened; 1/2 cup confectioners' sugar; 1 teaspoon finely grated lemon zest; 1 teaspoon pure vanilla extract; 1/8 teaspoon salt; 1 1/2 cups all-purpose flour; 4 large eggs, at room temperature; 2/3 cup granulated sugar; 1/4 teaspoon pure vanilla extract; 4 ounces bittersweet chocolate, coarsely chopped; 3 tablespoons water; 1 1/2 sticks (6 ounces) unsalted butter, at room temperature; Confectioners' sugar, for sifting; 1/2 cup granulated sugar; 2 tablespoons water