medium saucepan over medium heat, melt the butter. When it’s fully melted and just beginning to foam, sprinkle in the flour. Whisk constantly for 1–2 minutes, until the mixture is smooth and smells slightly nutty but has not browned deeply. This cooks out the raw flour taste.
Add the milk and thicken the sauce: Slowly pour in the milk while whisking continuously to avoid lumps. Continue to cook, whisking often, until the mixture comes to a gentle simmer
