Set the slow cooker to Low while you prep so it’s warm when the sauce goes in.
Heat a large skillet over medium-high. Add the ground beef and cook, breaking it apart, until mostly browned with some pink remaining, 5–7 minutes. Sprinkle in the paprika and red pepper flakes and cook 30 seconds to bloom the spices.
Push the beef to one side of the skillet. Add the onion to the open space and cook until translucent, 3–4 minutes. Stir in the garlic and cook 30 seconds more.
Pour in 1/2 cup of the beef broth to deglaze, scraping up any browned bits. Transfer the skillet contents to the slow cooker.
Stir in the remaining broth, crushed tomatoes, diced tomatoes, Worcestershire, Italian seasoning, bay leaves, and salt. Cover and cook on High for 2 1/2–3 hours or on Low for 5–6 hours, until the flavors are well combined.
Increase the heat to High if needed. Stir in the elbow macaroni, re-cover, and cook until the pasta is just tender, 20–30 minutes, stirring once halfway. If the mixture seems too soupy, uncover for the last 5 minutes to thicken.
Remove and discard the bay leaves. Turn off the cooker, fold in the cheddar until melted, and let stand 5 minutes. Taste and adjust salt before serving.