Trim off the stem and discolored leaves from the Brussels sprouts; cook in salted water for 15 minutes.
Drain and cover with boiling salted water.
Cook, uncoveredjust until tender, about 15 minutes.
Meanwhile, to make the sauce, melt the margarine in a pan.
Add the flour and salt and mix thoroughly.
Stir in the milk and bring to a boil, stirring occasionally.
Set aside over low heat until Brussels sprouts are cooked.
Drain Brussels sprouts and place in a heated serving bowl.
Pour sauce over vegetables.