Combine first 4 ingredients in a 4-quart casserole. Arrange chicken over vegetables. Drizzle with vermouth; sprinkle with salt, pepper, and nutmeg. Nestle garlic around chicken. Cover casserole with aluminum foil and casserole lid. Bake at 375° for 1 1/2 hours. Garnish with fresh tarragon, if desired; serve with French bread.