Into a medium sauce pan you will add six tablespoons of all purpose flour. While whisking your flour slowly add in two cups of milk. Whisk slowly so you don't get any lumps in the flour. Place your sauce pan on the stove with medium to low high. Whisk throughout the entire heating process or you could burn the milk on the bottom of the pan. It will then form into a thick paste which you will transfer to a bowl and let it cool slightly. With your mixer and mixing bowl add two cups of butter that is at room temperature. Mix for about five minutes scraping down the sides of the bowl every now and then. After five minutes have passed slowly add two cups of sugar while the mixer is on. Before you add your milk mixture that has cooled you'll add two teaspoons of vanilla. With the mixer going add the cooled milk mixture a tablespoon at a time. Now that all the ingredients have been added to the icing bring the speed up to medium for a couple of minutes. Next transfer the icing to a bowl and refrigerate for fifteen minutes only. It should be used right away.