Wash fillets and pat dry, then roll and skewer with wood picks or fold, in half crosswise. Arrange in large skillet. Add onion, parsley, thyme, wine, lemon juice and half of the grapes. Cover and bring to a boil. Reduce heat and simmer 5 minutes until the fish flakes easily with a fork. Remove the fish and grapes to a heatproof platter: remove the picks and keep warm. Measure juices and reduce to 1/2 cup if necessary. Melt butter in saucepan, and blend in flour. Add juices, half-and-half and any juices collected under the fish. Cook and stir until smooth and thickened. Pour the sauce over fish. Arrange remaining grapes around the fish on the platter and broil 1 minute until sauce bubbles and is tinges brown. Serve immediately.