Preheat oven to 375°F. Butter and flour 9-inch-diameter cake pan with 2-inch-high sides. Line bottom with parchment. Butter and flour parchment. Finely grind hazelnuts and 2 tablespoons sugar in processor. Place 2/3 cup ground-nut mixture in medium bowl; add flour and whisk to blend. Reserve remaining nut mixture for garnish. Using electric mixer, beat eggs and 2/3 cup sugar in large bowl until mixture is thick and slowly dissolving ribbon forms when beaters are lifted, about 8 minutes. Fold in flour mixture in 3 additions. Transfer batter to prepared pan. Bake cake until top is golden and tester inserted into center comes out clean, about 28 minutes. Transfer cake to rack. Cool in pan 10 minutes. Run small knife between pan sides and cake to loosen. Turn cake out onto rack; peel off parchment. Cool completely. Bring cream to simmer in large saucepan. Remove from heat. Add chocolate and whisk until melted and smooth. Pour into 13x9x2-inch glass dish. Refrigerate until ganache thickens to spreadable consistency, stirring occasionally, about 1 hour 30 minutes (ganache will resemble thick pudding). Transfer 3/4 cup chocolate ganache to small bowl; set aside for garnish. Cut cake horizontally into 2 layers (layers will be thin). Place 1 cake layer, cut side up, on platter. Spread 1/2 cup chocolate ganache over. Arrange sliced strawberries in slightly overlapping concentric circles over ganache. Spread 1/2 cup ganache over cut side of second cake layer. Place cake layer atop strawberries, ganache side down, and press slightly to adhere. Spread remaining chocolate ganache over sides and top of cake. Gently press reserved ground hazelnuts onto sides of cake. Transfer reserved 3/4 cup ganache to pastry bag fitted with medium star tip. Pipe 8 rosettes around top edge of cake, spacing apart. (Can be prepared 1 day ahead. Cover with cake dome and refrigerate. Let stand at room temperature 1 hour before continuing.) Starting 1/3 inch from stem end of whole strawberries, thinly slice strawberries lengthwise to tip. Press slices slightly to fan. Place fanned berries between rosettes on cake. Garnish with additional toasted hazelnuts, if desired.