In a 2 quart saucepan, melt the butter over medium heat. Add onions and stir until tender (do not brown). Slowly add flour while stirring. Stir slowly until thick. Keep stirring, gradually add the milk and continue until the sauce is smooth and creamy. Add salt, pepper, and seasoning. Remove from heat. Serve over seafood, chicken or vegetables. I like sauted shrimp and pasta with this sauce.