chocolates with coffee and butter in heavy medium saucepan over medium-low heat, stirring until smooth. Pour into large bowl. Cool. Mix in vanilla extract. Using electric mixer, beat yolks with both sugars in medium bowl until slowly dissolving ribbon forms when beaters are lifted. Fold yolk mixture into chocolate mixture. Fold in flour. Using electric mixer fitted with clean, dry beaters, beat whites in another large bowl until almost stiff. Fold 1/4 of whites into chocolate mixture to lighten. Gently fold in remaining whites. Gently pour batter into prepared pan. Bake until toothpick inserted in center comes out with moist crumbs still attached, about 45 minutes. Transfer to rack and cool (cake will fall). (Can be prepared 1 day ahead. Cover cake in pan with plastic wrap and let stand at room temperature.) Run small knife around cake pan sides to loosen if necessary. Release pan sides of cake. Invert cake onto plate. Place stencil or doily atop cake. Sift powdered sugar over. Remove stencil from cake and serve.