2 tablespoons butter
1 1/2 tablespoons flour (more for a thick sauce)
1/4 teaspoon salt
1 cup milk
Melt 2 tablespoons butter in a pan, take off the fire and blend in 1 1/2 tablespoons flour. If you wish a thick sauce, use 2 tablespoons of flour. There must always be enough butter to moisten the flour. Add 1/4 teaspoon salt and a cup of milk. You'd better heat the milk, do not boil, then add a little bit at a time, stir thoroughly, put back over, low fire, and stir constantly till it comes to a boil.
Unless you want a 'gob" of sauce, 1 tablespoon of flour makes enough.