In a pot under medium low heat, continuously whisk together flour and milk until you get a pudding-like consistency. It'll be ready when you can lift the whisk and drip some of the mixture and it'll leave a trail. (About 10 minutes).

Remove from heat and let cool, whisking every so often to get prevent a skin from forming and to speed up the cooling process.

Meanwhile, beat 2 cups butter (chopped into smallish pieces) with vanilla flavouring and 2 cups sugar until light and fluffy.

Add the completely cooled flour/milk pudding 1 tbsp at a time, or in a very slow, thin stream into the butter mixture, beating constantly. Once you slowly incorporate all of the flour mixture, you'll have a beautifully light and fluffy frosting.

Keep frosting and frosted cake in a cooled place, this frosting isn't that great in the heat.