If you like a deeper flavor, brown the ground beef in a skillet over medium-high heat until no longer pink. Drain excess fat.

Transfer the browned beef to the slow cooker. Add chopped onion, minced garlic, ketchup, brown sugar, mustard, Worcestershire sauce, apple cider vinegar, chili powder, smoked paprika, salt, pepper, and beef broth. Stir to combine.

Cover and cook on low for 7 hours (420 minutes). The slow cooker will meld the flavors and break down the meat.

After the cooking time, give the mixture a good stir. If you prefer a thicker sauce, whisk 2 tbsp cornstarch with 2 tbsp cold water, stir it into the slow cooker, and let it thicken for about 10 minutes on low.

Warm the hamburger buns in the oven for a minute or two, then spoon the sloppy joe mixture onto each bun. Sprinkle shredded cheddar cheese on top if desired.

Use a food thermometer to verify the internal temperature of the beef mixture before serving.