How to Make It
Cream margarine and cream cheese at medium speed of a heavy-duty stand mixer until light and fluffy. Add vanilla and salt; beat well. Gradually add sugar and milk, beating at low speed. Increase speed to high, and beat until well-blended and spreadable.
Note: If frosting is made ahead and chilled, add a small amount of milk, a teaspoon at a time, to soften. Beat until spreadable.