Preheat oven to 325 degree F. In a 15x10x1-inch baking pan combine walnuts, almonds, and hazelnuts. Bake, uncovered, for 5 minutes. Add pine nuts to the baking pan and bake about 8 minutes more or until all the nuts are toasted. Let the nuts cool. Reserve 1 cup whole nuts. By hand, coarsely chop remaining nuts.
In a large bowl combine the whole and chopped nuts, candied fruit, raisins, and orange peel. In another bowl stir together the flour, cocoa powder, grated chocolate, cinnamon, pepper, cloves, nutmeg, salt, and cardamom. Add the dry ingredients to the fruits and nuts, tossing to coat well.
In a medium saucepan bring the honey and sugar to boiling, stirring to dissolve the sugar. Boil gently for 3 minutes. Stir in the grape juice or water. Pour the hot syrup over the fruit and nut mixture, stirring to coat (batter will be thick).
Press the mixture into a greased 10-inch springform pan. Bake about 30 minutes or until just firm in the center. Cool in pan on a wire rack for 15 minutes. Loosen from sides of pan. Cool completely in pan.
To serve, use a sharp knife to cut the panforte into thin wedges. Serve when cool or wrap and store several days before slicing. Makes 24 servings.