Add the beef and onions to a Dutch oven/soup pot over medium-high heat. Cook for 7-10 minutes, breaking the meat up with your spoon as you go along. If there's a lot of excess fat, spoon most of it out.
Stir in the garlic, chili powder, smoked paprika, and green chilies.
Add in the beef broth, tomato sauce, and cream, and increase the heat to high.
Once it just starts to boil, add in the macaroni. Reduce the heat so it's rapidly simmering (I usually keep it around medium heat), and cook, uncovered, for 13 minutes or until the pasta is cooked and the liquid has reduced. Stir it every couple minutes to prevent the pasta from sticking to the bottom of the pot. If the liquid seems to be disappearing too quickly before the pasta is cooked or if you want it more soupy, add in 1/2 cup more broth and/or lower the heat.
Take the pot off the heat and stir in the cheese. Season with salt & pepper as needed. If you need the liquid to absorb a little more prior to serving, simply cover the pot and let it sit for a few minutes. Optional: if you want a melty cheese layer on top, sprinkle on an extra 1/2 cup or so of cheese and cover the pot until it melts.