Many people have been eating well-done burgers their whole life. In the 1960s, my mother realized that rare ground beef was probably not a good thing to eat. She was years ahead of her time. We now know that ground meats can harbor pathogenic bacteria that can, and does, make people sick. There have been many foodborne illness outbreaks linked to undercooked ground beef. The most famous was the 1993 Jack in the Box E. coli outbreak that sickened 400 people and killed three children. The burgers were not properly cooked in that outbreak; it changed the way many people looked at fast food.
So when we cook burgers at home, we make sure that they are cooked to at least 160 F as checked with a food thermometer. The problem is, this can be difficult to do on the grill. Getting a burger to well done without burning or charring the outside, or turning it into a dry lump, is very difficult. But there are other ways to get around this problem. You can bake your burgers. Or you can cook them in the slow cooker!
The slow cooker is the perfect environment for this task. The low, moist heat cooks the meat thoroughly but doesn't dry it out. The sauce is savory and spicy and the perfect complement to the tender meat.
We like to serve these burgers on toasted English muffins, topped with sliced avocados and a creamy mustard sauce, but you can serve them any way you'd like. Enjoy every bite.
In a large bowl, combine the onion, garlic, 3 tablespoons of the mustard, 3 tablespoons of the tomato sauce, and 1 tablespoon Worcestershire sauce and mix well. Add the ground beef and mix gently but thoroughly until combined.
Make six patties with the ground beef mixture.
Combine the remaining mustard, tomato sauce, Worcestershire sauce, and chili sauce in a medium bowl.
Layer the ground beef patties with the sauce in a 4-quart slow cooker, making sure to get enough sauce between the burgers so they don't stick as they cook.
Cover and cook on low for 5 to 7 hours or until the burgers register 160 F as tested with a reliable meat thermometer. Remove the burgers from the slow cooker using a spatula or slotted spoon to drain off most of the sauce.
Assemble the burgers with the English muffins, avocados, any remaining sauce if you'd like, or other condiments and serve.