Whipped Buttercream Frosting

Instructions

1. In a small saucepan, make a roux by whisking sifted flour into milk over medium-low heat, whisking constantly until it thickens to a paste. Don't let it overcook or get lumpy.
2. Remove from heat and stir in vanilla.
3. Let cool to room temperature. If your mixture is warm it will melt your butter and you'll end up with runny frosting.
4. While the mixture is cooling, cream together the butter, sugar, and salt until light and fluffy, on medium high / high for about 5 minutes. Pause occasionally to scrape down the sides of the mixing bowl with a spatula: this will help you fully incorporate the butter and sugar and void a gritty frosting. If you don't beat long enough, you'll end up with a gritty frosting.
5. Beat in the cooled / room-temperature flour-milk-vanilla mixture for at least 5 more minutes on medium-high / high until it looks like whipped cream. It may look separated at first but keep beating until it comes back together.