Cooked Not-Too-Sweet Buttercream

This frosting is light, fluffy, silky, buttery and, unlike the vast majority of buttercream frostings, not too sweet. 

10 tbsp (1/2 c + 2 Tbsp) all-purpose flour
2 c granulated sugar

1/4 tsp salt 

2 c milk
2 tsp vanilla extract
1 c butter, softened

In a medium saucepan, whisk together sugar, flour and salt. Whisk in milk until smooth. Cook over medium heat, whisking constantly, until it comes to a boil. Continue whisking for 3-5 minutes, until it thickens considerably and loses the raw flour taste. Transfer to a clean bowl; let cool completely, either in an ice bath or in the refrigerator. 

Beat butter in a stand mixer until lightened and fluffy, at least 30 seconds. Add flour mixture and vanilla. Beat until incorporated fully, then continue to beat until frosting is light and fluffy.