Melt the butter in a medium pot or saucepan set over medium heat. Once the butter has melted, add the flour, whisking continuously until the flour has fully absorbed the butter, creating a thick paste. Continue mixing for about two minutes until the mixture is smooth and thickened, then add the salt, cumin, and smoked paprika, mixing well.
Whisking continuously, slowly add the milk. Mix well to incorporate the milk with the roux, then heat, stirring often to prevent scorching, until the milk bubbles. Bring to a gentle simmer, but do not boil.
Reduce the heat to medium-low (or lower) and continue to simmer, stirring continuously, for 6-8 minutes or until the sauce is thick enough to coat the back of a spoon.
Reduce the heat to low, then add the cheese a handful at a time, stirring well between each addition, then immediately remove from heat.
Season with additional salt and black pepper to taste. Best served immediately.