Crawfish Vol-Au-Vent

1 cup onions -- chopped
1/4 cup onion tops -- chopped
1/2 lb butter
3/4 cup all-purpose flour
1 quart milk
1/2 cup corn
1/2 cup potatoes -- diced
Saute onions in butter. Stir in flour and cook over low heat, stirring
often so flour doesn't burn, about 5 minutes. Add milk. Stir and cook
until flour is dissolved. Add corn and diced potatoes. Stir and cook
about 2-3 minutes. Add: 1 lb. crawfish 1/2 Tbsp. salt 1 Tbsp. pepper
Simmer, stirring often, until crawfish is done.