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