In a large saucepan combine the flour, sugar and salt. Stir to combine. Toast over medium heat for 30 seconds to 1 minute.

Slowly whisk in the milk, adding just a little at a time making sure it is completely incorporated before adding more. This will keep the frosting lump free just like with a roux.

Switch from the whisk to a silicone spatula and stir constantly over medium heat. I like to use a zig-zag pattern across the pot and then around the edges. I repeat this same pattern to ensure that I am scraping the whole bottom and none will burn. It is the same technique that I use for vanilla pudding or lemon curd!

Continue cooking until the flour mixture has thickened and will drop off a spoon in clumps rather than pour off in a stream. This thickness will determine the consistency of your final frosting. A thicker base will make a pipeable frosting that holds beautiful lines and details even in high heat and humidity.

Remove from the heat and scrape into a bowl with the spatula. Cover the top with plastic wrap that is touching the surface, and allow to cool at room temperature until it is no longer warm to the touch. You can speed this up by cooling it in 20 minute intervals in the refrigerator, stirring and repeating until it is body temperature.

In the bowl of a stand mixer fitted with the whisk attachment, beat the butter on medium-high speed until fluffy and almost white in color.

With the mixer running, add a spoonful of the flour mixture and allow it to beat in fully before adding the next. Stop the mixer to scrape in the last of the flour mixture and scrape down the sides and bottom of the bowl.

Add the vanilla extract and continue to whisk on high until it holds stiff peaks.

Transfer to a piping bag or spread on cakes.