In a small mixing bowl mix together the mustard, pepper, thyme, rosemary, garlic salt. Rub the meat with the mustard mix
Heat some vegetable oil in a skillet on high til sizzling. Sear all sides of the roast 30-45 seconds per side.
Place the vegetables and chopped garlic in a slow cooker. Add the roast once seared and pour over the beef broth. Cook on high for 4 hours to an internal temperate of around 145F
Use a pair of tongs to remove the roast from the cooker. Use a slotted spoon to remove and set aside the vegetables.
Melt the butter in a large pot, whisk in the flour to form a roux. Strain the roast juices from the slow cooker through a sieve into the pot. Return the vegetables and roast to the slow cooker and cover to rest.
Add worchestershire sauce and pepper to the gravy, bring to a simmer and whisk til the flour dissolves and the gravy thickens. Reduce heat to low and cover.