In a medium saucepan, melt the butter over medium-high heat.

Add the all purpose flour and cook, stirring constantly with a silicone whisk, until bubbly and pastelike, with no lumps remaining.

Add the whole milk, bring to a boil, and whisk until well-combined. Cook, whisking continually, until thickened, about 30-45 seconds.

Reduce heat to low. Add the cheese in 3 additions and continue whisking until fully melted and smooth.

Whisk in the hot sauce and kosher salt. Taste and adjust, adding more hot sauce or salt as desired.

Serve immediately. Store leftover nacho cheese sauce in the refrigerator for up to 3 days.