In a skillet over medium heat, brown ground beef and onion; drain off any grease.
Add taco seasoning, Rotel, beef broth, and macaroni; stir until well blended. Heat to boiling. Reduce heat to simmer and cover pan.
Simmer 12-14 mins until macaroni is tender.
While the hamburger mixture simmers, melt the 2 Tbsp butter in a saucepan. Whisk in the flour and cook 2 minutes until fragrant and light brown in color.
Slowly whisk in the milk and bring to a boil. Cook while whisking until smooth and thickened to the consistency of gravy.
Remove from heat and blend in the shredded cheddar cheese until melted. Add the salt and pepper to the cheese sauce. Pour the cheese sauce over the cooked hamburger mixture. Stir gently to combine.