Prepare a fire and let it cook down to hot coals. If you'll be using charcoal for the Dutch oven, start a chimney of 24 coals.
Set the Dutch oven over hot coals or low flame and add the ground beef and sausage. Cook, stirring frequently, using a wooden spoon to break up the meat into small pieces, until browned, about 10 minutes.
Add the onion and season with salt and pepper. Cook, stirring occasionally, until the onion is softened, about 10 minutes.
While the onion is cooking, stir the ricotta, egg, and Parmesan together in a medium bowl. Season with salt and pepper.
Stir the marinara sauce into the cooked meat mixture. Scoop out most of the sauce into a large bowl, leaving a thin layer on the bottom of the Dutch oven.
Arrange a layer of noodles over the sauce. You'll need to break some of the noodles to make everything fit, but it's fine to puzzle together small pieces as you go.
Spread ⅓ of the ricotta mixture over the noodles, then dollop ¼ of the sauce on top of that. Cover with ½ cup of mozzarella cheese. Repeat the layering two more times.
Finish with a layer of noodles, the remaining sauce, and the remaining mozzarella cheese.
Cover the Dutch oven with its lid and set it on top of 8 coals. Place 16 coals on the lid and let it cook, replacing the coals as needed. Cook until the noodles are tender, the sauce is bubbling, and the cheese is melted, about 50 minutes.
Remove from the fire and let rest at least 10 minutes before cutting and serving.