In a medium saucepan, whisk one cup of milk with 5 tablespoons of flour. Heat over medium until the mixture begins to sputter, whisking constantly. Continue to stir as the mixture thickens. You will know it’s done when it reaches the consistency of thick cake batter, after about 7 minutes of heating and whisking. Stir in 2 teaspoons vanilla extract and set aside to cool COMPLETELY.

Now, in the bowl of a stand mixer fitted with a whisk attachment, or using a hand held mixer, beat 2 sticks of softened butter (1 cup) with 1 1/4 cups of granulated sugar until light, fluffy, and white in color, about 3 solid minutes of beating on medium-high speed. You want the sugar to be totally incorporated into the butter.

Be sure that the milk/flour mixture has completely cooled, and add it to the butter/sugar mixture. Beat all ingredients for about 1 minute on high speed, scraping down the bowl halfway, until they are smooth and well blended. The frosting should be as light and fluffy as whipped cream.