I made a cheese sauce in the double broiler - so over, not in boiling water- the other day that turned out pretty good. I put chunks of cheddar cheese and once they started melting I added milk, and kept stirring and adding milk until it was the right consistency.
You really have to keep it over the boiling water until you are ready to serve or use it, otherwise the texture goes weird as it cools.
If you want to make it spicy, you can add some canned peeled tomatoes along with some the juice, and a few chopped jalapenos.