In a large saucepan, combine the fish heads and bones, the onion with the clove, carrot, celery, bay leaf, peppercorns, salt, and wine. Add 1-quart water and bring to a boil. Boil for 30 minutes, until the liquid is reduced by a little less than half. Strain the liquid into a small saucepan and discard the solids.
Season the sole fillets with salt and pepper on both sides. Lay a few spinach leaves on 1 side of each fillet. Divide the crab meat evenly among the four fillets and spread it over the spinach. Top with some of the raisins and pine nuts and roll up each fillet. Secure with a toothpick or string.
In a mortar and pestle, combine the saffron strands with the sugar and crush together to form a sandy paste. Set aside.
In a 12 to 14-inch saute pan, heat the olive oil over high heat until almost smoking. Add the stuffed sole fillets and cook on all sides until light golden brown, about 5 minutes. Meanwhile, bring the fish broth to a boil. Remove the fish bundles to a plate and add the boiling fumet, scraping the bottom of the saute pan with a wooden spoon to dislodge any browned bits. Add the saffron mixture and the Prosecco and bring to a boil. Cook until reduced by half, then add the butter, bit by bit, until it is all absorbed. Return the fish bundles to the pan to heat through, then serve immediately.
Recipe copyright 2001, Mario Batali. All Rights Reserved.