Melt the butter in a medium saucepan over medium heat. Once melted, whisk in the flour and cook for about 1–2 minutes until it forms a smooth paste and turns slightly golden.

Slowly pour in the warm milk while continuously whisking. This helps prevent lumps and keeps your sauce smooth. Cook for 3–4 minutes until the mixture thickens.

Lower the heat and add the shredded white cheddar and American cheese slices. Stir continuously until the cheese melts completely and the sauce becomes silky.

Add salt, paprika, garlic powder, and cayenne (if using). Stir well and taste to adjust seasoning if needed.

Remove from heat and serve immediately over burgers, fries, or hot dogs while it’s warm and pourable.