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