Combine dry milk and water, and set mixture aside.
Melt the margarine in a small heavy saucepan over medium-low heat, and add flour, salt, and pepper. Cook margarine mixture 1 minute, stirring constantly with a whisk. Gradually add milk mixture to saucepan, stirring constantly. Cook, stirring constantly, 10 additional minutes or until thick and bubbly. (Mixture will be very thick.)
