Chocolate Torte (1+)

Position rack in center of oven and preheat to 350F. Butter 9-inch-diameter springform pan with 3-inch-high sides. Line bottom with waxed paper round. Finely grind walnuts with flour in processor; set aside. Stir chocolate in top of double boiler over simmering water until melted and smooth. Remove chocolate from over water. Cool chocolate slightly. Using electric mixer, beat butter and 7 tablespoons sugar in large bowl until light and fluffy. Beat in melted chocolate. Add yolks 1 at a time, beating well after each addition. Continue beating until smooth and light, about 3 minutes. Mix in ground walnut mixture. Using electric mixer fitted with clean dry beaters, beat whites in another large bowl until beginning to form soft peaks. Gradually add remaining 7 tablespoons sugar and beat to soft peaks. Stir 1/4 of whites into batter to lighten. Fold in remaining whites. Pour batter into prepared pan; smooth top. Bake until tester inserted into center comes out with some moist crumbs attached, about 40 minutes. Cool cake in pan on rack 10 minutes. Run sharp knife around pan sides to loosen cake. Release pan sides and cool cake completely (cake may fall as it cools). (Can be prepared 2 days ahead. Cover and let stand at room temperature.) Transfer cake to platter. Sift powdered sugar over cake. Cut into wedges and serve.