Wash and dry sole. Set fillets in baking dish, side by side. Sprinkle on minced onion, lemon juice, and wine. Cover and bake 15 minutes at 350 degrees. Meanwhile, slightly bruise grapes and marinate in cognac. Make a sauce of butter, flour and cream; add mixed vegetable seasoning. Combine sauce with grapes and cognac. Pour over sole fillets and return to oven for 5 minutes.