1. In a saucepan, melt the butter. Add the onion and cook for 2 minutes. Add the flour and curry; mix to make a roux. Pour in the milk, stirring constantly; reduce heat to low and let thicken for 5 minutes, stirring. Season with salt and pepper.
 
2. In a saucepan, cook the mussels in the broth for 5 minutes, covered. Add the bechamel, garlic powder, and green onions.
 
3. Season generously before serving very hot.