Melt margarine in a medium saucepan over med heat. Add flour until bubbly. Slowly add soymilk. Bring to a boil stirring constantly (a whisk works good) . Grate cheese and add slowly stirring until you get the consistency desired. Add salt to taste. Note: If the mixture doesn't get thick enough before you add the cheese, whisk in a tbs. flour.
Use this sauce on nachos, mac and cheese and baked potatoes.