Rinse fish thoroughly in cold water; pat dry. Brush fish with lemon juice; sprinkle with salt and pepper. Set aside.
Cut out a 9-inch circle of unglazed brown paper. (Do not use recycled paper.) Puncture paper once with a fork; grease heavily, and set aside.
Melt 1 1/2 teaspoons butter in a 9-inch skillet; add carrots and onions. Cover, and cook over medium heat until vegetables are tender; uncover, and dot with 3 teaspoons butter. Place fish on top of vegetables; add parsley and wine. Cover skillet with prepared paper.
Bring mixture to a boil; reduce heat, and simmer 10 minutes or until fish flakes easily when tested with a fork. Transfer fish and vegetables to a warm serving platter, reserving wine sauce in skillet.
Combine flour and softened butter in a small mixing bowl; mix well, and stir into remaining wine sauce in skillet. Cook over low heat until thickened.
Pour wine sauce over fish and vegetables. Serve immediately.