3 T Flour
1/2 C milk (whole milk is best, but I used non-fat when it's all I have and it's actually fine)
1/2 C real butter
1/2 C sugar (that's granulated sugar, not powdered sugar)
1 t vanilla extract, or other flavor if you wish.
Whisk together the flour and the milk. Heat in a small sauce pan on medium heat. Whisk continuously until it starts to thicken. (It will get really thick - goopy even!) Let it cook, while stirring, until it looks like pudding (you should be able to see the bottom of the pan when you stir it). Push it through a mesh strainer and then let it cool completely to room temp. or chill it in the fridge. It needs to be cooled completely.
It an electric stand mixer, using the whisk attachment, beat the butter and the sugar for a minute or two until well combined and fluffy. Then while beating, add in the thickened milk mixture and the vanilla. Beat on the highest speed you can get to without it spraying all over the place for 7 minutes.
You will be scared because it will look like a weird goopy mess at first and you'll wonder what on earth you did wrong. Keep beating and something amazing happens. It goes from that goopy mess to something thick, velvety smooth, and perfectly fluffy.
One batch makes enough to frost 12 cupcakes . Use this to top your peppermint fudge cupcake jars.