Place egg whites in a large bowl; let stand at room temperature for 30 minutes. Line the bottom of a greased 9-in springform pan with waxed paper; grease the paper and dust with cocoa.
Melt 6 ounces bittersweet chocolate in short bursts in the microwave. I did 30 seconds then 20 seconds. Stir well and set aside to cool.
Place hazelnuts and brown sugar in a food processor; cover and process until ground. Set aside. In a second large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add egg yolks, 1 at a time, beating well after each addition. Beat in the melted chocolate, espresso powder, extract and salt. Gradually add hazelnut mixture.
In the first large bowl, with clean beaters beat egg whites until stiff peaks form. Fold into batter. Spread into prepared pan. Place pan on a baking sheet.
Bake at 375° for 35-45 minutes or until a toothpick inserted in the center comes out with a few moist crumbs. Cool on a wire rack to room temperature. Remove side of pan and invert onto a serving plate.
To make ganache, place chocolate in a small bowl. In a small saucepan, bring cream just to a boil. Pour over chocolate; whisk until smooth. Cool, stirring occasionally, to room temperature or until ganache reaches a spreading consistency, about 30 minutes.
Spread ganache over top and side of cake; press almonds or pecans around the side. Cover and refrigerate for 30 minutes or until set.