1. Heat oil on a medium flame.
2. Sauté onion until translucent, then add garlic and sauté for two minutes.
3. Push onions and garlic aside, and melt butter.
4. When butter is melted, add flour and mix until it forms a roux.
5. Add milk to the pan, and mix with sautéed onions and garlic and roux.
6. When combined, add cheese, one slice at a time, until sauce thickens and cheese is completely melted.
7. If you like a thinner sauce, add a bit more milk until it gets to the desired consistency.
8. Add diced jalapeno pepper and cayenne pepper and stir.
9. Serve immediately with pita chips.