Line bottom with parchment. Wrap ouside of pan with foil. Melt chocolate in top of double boiler over simmering water, stirring until smooth. Set aside to cool. Using elecric mixer, beat butter and one third cup sugar in large bowl to blend. Mix in cornstarch, espresso powder and salt. Beat in egg yolds, 1 at a time. Mix in melted chocolate. Using clean dry beaters, beat egg whites in another large bowl with one third cup sugar until stiff but not dry. Fold whites into chocolate mixture in 2 additions. Transfer to prepared pan. Bake cake until set and tester inserted into center comes out with moist crumbs attached, about 50 minutes. Cool cake completely on rack (cake may fall and appear cracked). Refrigerate until well chilled, about 4 hours. Preheat oven to 300 degrees. Bake cake uncovered just until warm, about 20 minutes. Cut around cake to loosen. Release pan sides. Cut warm cake into wedges. Garnish with pieces of brittle and serve. ----