In a bowl, mix together the salt, pepper and garlic.
Place your chuck roasts on a baking sheet, lather with yellow mustard and generously season all sides in order to completely cover the roasts.
Place them in the fridge, uncovered, for at least 4 hours but ideally overnight.
Preheat your smoker to about 250 degrees F. Add some wood chips or wood chunks if desired for extra smoky flavor.
Pull your chuck roasts out and place on the smoker to cook until 165 degrees F internal (about 3 hours).
Once the chuck roasts have hit temperature, pull them out and place in a large foil bin.
Fill into the bin your beef broth, beef tallow and sliced white onions. The liquid in the bin should come up to 50% of the chuck roast’s height, so add more or less if necessary.
Tightly cover your bin with foil and place back on the smoker at 300F to smoke until the meat is tender to probe and shreddable (another 3-4 hours).
Once the chuck roasts are done, pull them off and let them rest for 20 minutes.
After the rest, pull the chuck roasts out and shred them up. (Optional: strain and simmer the au jus down by half for a dipping sauce)
Build your melt with thick cut texas toast, slice of cheddar cheese, some bbq sauce, handful of shredded beef, more bbq sauce, another slice of cheddar beef and another thick cut sliced brioche.
Add the melts to the skillet and toast the bread till golden brown.
When the melts are done, pull off and slice. Add to a bowl of bbq sauce or strained broth from the crutch. Dip the patty melts in the sauce for serving. Enjoy!