Whisk the raw beef into the cold broth in a 7-quart crockpot until the meat is broken into very fine bits.
Stir in the onion, garlic, tomato sauce, chili powder, paprika, cumin, Worcestershire and salt.
Cover and cook on low for 6 hours, stirring after 2 hours and again after 4 hours to keep the texture even.
Confirm the beef has reached 160°F, skim the surface fat, and stir in the mustard.
Cook uncovered on high for 30 minutes until a spoon dragged through the sauce leaves a trail for 2 seconds, then switch the cooker to warm.