Melt the butter in a saucepan over medium heat. Sauté the jalapeno pepper (If using) for about 3 minutes, then whisk in the flour and stir for about 1 minute until bubbly and golden.
Gradually whisk in the milk. Add in the shredded cheese, paprika, and chipotle (if using); whisk until smooth. Bring to a low simmer. The sauce should start to thicken. Season with salt and pepper to taste.
Once it's creamy and thick, remove from heat and spoon over the tortilla chips. Garnish with lettuce and tomato.
**Queso can be made first and reheated right before you're ready to serve.