Step 4
Melt butter in a saucepan, and cook and stir the onion, garlic, and chipotle chiles until the onions are translucent, about 5 minutes. Whisk in flour, 1 tablespoon at a time, and let cook for about 3 minutes, whisking constantly to avoid burning. Whisk in the hot milk, 1/2 cup at a time, and stir in paprika, salt, and pepper. Bring the mixture to a simmer (do not boil), whisking constantly until thickened, about 2 minutes. Whisk in the cheeses, about 1/2 cup at a time, and stir until the cheeses have melted and the sauce is thick and smooth.