01 - Melt the butter in a medium saucepan over medium heat. Add the flour and whisk constantly for about 1 minute to form a smooth roux, taking care not to let it brown.
02 - Gradually whisk in the milk. Cook, stirring frequently, until the mixture thickens and just reaches a simmer, approximately 2–3 minutes.
03 - Reduce the heat to low. Add the Dijon mustard, hot sauce, garlic powder, cayenne (if using), salt, and pepper. Stir thoroughly to combine all seasonings.
04 - Add the grated cheddar cheese one handful at a time, whisking until completely smooth and melted before adding more cheese.
05 - Once all cheese is incorporated and the sauce is silky smooth, taste and adjust seasoning as desired. Serve immediately while hot.