In a large sauce pan on medium heat start by adding tallow, followed by flour.
Once silky smooth, add 3 1/2 cups by milk. Stir until smooth, add cream cheese. Stir some more until smooth, add seasonings. Add cheese, stir until smooth.
(Now this is where you can either save it and make the rest of the mac & cheese the next day or later in the week, or just continue on)
Add cooked al dente pasta to a large grill-safe dish.
Add about half of the Bechamel sauce, followed by shredded cheese, and repeat. The more the merrier. Top with more sauce and cheese, and a little extra brisket rub or cracked black pepper.