Take and melt the margarine. Add the vanilla and 1/4 cup milk. Then start adding the powder sugar. When it gets to thick add a couple more Tblsp. milk. If too thin just add a bit more powder sugar. Get to the consistency that you like.
Madagascar Vanilla (purchase at Chefs Catalog) Of all the vanilla's I've used this is my favorite. Once you've tried it you won't go back!