Melt the butter in a saucepan medium heat. Whisk in the flour 1 tablespoon at a time and cook, whisking constantly, until the roux is thick and forms a ball, for about 4 to 5 minutes.
Remove from the heat or incorporate some immediately into a dish you’re preparing. If you prefer, allow the roux to come to room temperature and refrigerate it, covered, for a week or two.
Yield: about 3/4 cup