Tangy with vinegar and sweet with dried currants, the marinade for this fish is called saor in Italian. The dish is ideal as a first course and wonderful as part of the multicourse Christmas Eve feast. Sole may be substituted for flounder, if you prefer.
Season fish with salt and pepper; dredge with flour, patting off excess. In a medium saute pan, heat 1 cup olive oil over medium-high heat. When oil is shimmering, fry fish until golden on both sides. Transfer fish to a nonreactive serving bowl just large enough to hold it in one layer; set aside. Discard oil in pan. Add remaining ¼ cup oil and onions and cook over medium heat until onions are translucent. Add garlic and bay leaves and cook 1 minute. Add vinegar and vermouth, then stir in currants, pine nuts, and sugar and bring to a boil. Reduce heat and simmer 5 minutes. Remove bay leaves and pour marinade over fish. Let cool to room temperature, then cover and refrigerate 24 hours before serving.