2 tablespoons unbleached all-purpose flour
  Salt and freshly ground black pepper
4 fillets fresh mahi-mahi (skinless (1-1/4 to 1-1/2 pounds total))
3 tablespoons olive oil
3 tablespoons finely minced shallots
1/2 cup champagne, sparkling wine, or fruity white wine (such as muscadet or gewürtztraminer)
2 tablespoons heavy (whipping) cream
1 1/2 cups champagne grapes or other small grapes (stems removed)
2 tablespoons unsalted butter (cut into 4 pieces, at room temperature)
  Salt and freshly ground black pepper (to taste)