Start by cutting the jalapeno in half and taking the seeds and rib out. If you like it spicy then by all means keep the seeds in and broil the jalapeno whole. Broil the jalapeno in the oven for about 10 minutes or until the skin gets nice and charred (rotate the pepper to ensure all sides are charred). The cooking time could change depending on how close your rack is to the broiler so keep an eye on it. When the jalapeno is done take a paper towel and pull the skin off then mince and set aside. (See note)
While the jalapeno is broiling take a box grater and shred the cheddar cheese put it in a small bowl and set aside. (See note)
In a medium sauce pan add the butter and flour. Whisk until combined and cook the butter and flour mixture for 1-2 minutes. This is going to cook off the flour taste. That wouldn’t be good in the sauce. Then add the milk and whisk occasionally. It will take about 5-7 minutes for the sauce to thicken.
Add the shredded cheese, the broiled jalapeno and the paprika. Whisk until the cheese is melted and the sauce is nice and thick. Pour over your favorite nachos. Enjoy!