Melt the 2 tbsp butter in a saucepan over medium heat, whisk in the 2 tbsp flour, and cook for about 1 minute until lightly golden.

Whisk in the 1 1/2 cups milk in two additions and simmer for about 4 minutes, stirring often, until it coats the back of a spoon.

Lower the heat and stir in the 8 oz cheddar and 4 oz American cheese a handful at a time, along with the 1/2 tsp mustard powder, 1/4 tsp garlic powder, 1/4 tsp smoked paprika, 1/4 tsp salt, and cayenne if using, until smooth.

Taste and adjust salt, then pour into a bowl and serve warm.