In a bowl, whisk the eggs and brandy or cognac together until foamy and add to the chocolate and hazelnuts. Gradually add about 1/4 of the melted chocolate mixture to the egg yolks, stirring constantly. Pour into the prebaked tart shell and bake until a skewer comes out of the center clean, 35 to 40 minutes. Remove the tart from the oven and let cool 15 to 20 minutes until warm. Cook over medium-low heat, stirring constantly for 3 to 5 minutes until mixture begins to thicken; remove from heat. In a medium bowl stir together flour, 1/4 cup sugar, and salt. Spread 1/2 cup of the chocolate mixture in bottom of cooled crust. In a small bowl stir together 2 eggs yolks and ice water. Stir egg mixture back into the pan of hot chocolate cream. Use a pastry blender to cut in butter until pieces are pea size. Add to the chocolate. Stir in nuts.