01 - In a medium saucepan over medium heat, melt the butter. Add the flour and whisk constantly for about 1 minute to form a roux, without letting it brown.
02 - Gradually whisk in the milk. Cook, stirring frequently, until the mixture thickens and just comes to a simmer, 2–3 minutes.
03 - Lower the heat to low. Add the Dijon mustard, hot sauce, garlic powder, cayenne if using, salt, and pepper. Stir to combine.
04 - Add the grated cheddar cheese a handful at a time, whisking until smooth and fully melted before adding more.
05 - Once all the cheese is incorporated and the sauce is smooth, taste and adjust seasoning as needed. Serve hot.