*This frosting takes a bit of advance planning since the frosting needs time to cool so plan ahead!
*Makes about 4 cups frosting (plenty for two 9-inch cake layers)
*Best if used while fresh, because once it is refrigerated, it won't re-whip properly. It will taste amazing for several days.
1 1/2 cups granulated sugar
1/4 cup all-purpose flour
3 tablespoons cornstarch
1/4 teaspoon salt
1 1/2 cups milk (I used 1%)
2 teaspoons pure vanilla extract
24 tablespoons (3 sticks) butter, cut into 24 pieces and softened at room temperature
In a medium bowl, combine the sugar, flour, cornstarch and salt. Slowly whisk in the milk until the mixture is smooth. Place a fine-mesh strainer over a medium saucepan and pour the milk mixture through the strainer into the saucepan. Cook the mixture over medium heat, whisking constantly, until the mixture boils and is thick enough that it starts to become difficult to easily whisk. This could take anywhere between 5-10 minutes, depending on your stove, heat, etc. It should bubble quite a bit at the end (be careful of the splatters - it's hot) and thicken considerably.
Transfer the mixture to a clean bowl and cool to room temperature. I refrigerated my initial mixture overnight. If you do this, make sure to pull it out in time to let it warm back up to room temperature. If you try to proceed with the rest of the recipe and the mixture is too cold, the butter won't absorb into the frosting like it should.
Once the frosting is completely cooled to room temperature (it should have no hint of warmth at all), beat the mixture with the vanilla on low speed until it is well combined, about 30 seconds (a stand mixer will work best for this). Add the butter, one piece at a time, and beat the frosting until all the butter has been incorporated fully, about 2 minutes. Increase the speed to medium-high and let the mixer work it's magic. Beat the frosting for five minutes, until it is light and fluffy. Let the frosting sit at room temperature until it is a bit more stiff, about 1 hour.
adapted from melskitchencafe.com