Place your roast in the bottom of your crock pot or slow cooker.

In a bowl, mix 1 cup cold water, brown gravy mix, worschestersire sauce, garlic powder, salt, and pepper. Whisk until combined.

Pour mixture over roast and place lid on slow cooker. Set to cook on low.

Let roast cook 6-8 hours until it falls apart easily with a fork.

Remove roast to a cutting board to shred.

With remaining drippings and gravy in the slow cooker, add 1 cup hot or boiling water and Dijon mustard. Whisk to combine well. Set slow cooker to high to keep nice and hot.

Toast your sandwich rolls with a bit of butter under the broiler in the oven or on a hot skillet. Fill each roll with meat, a slice of cheese, and place top bun on to allow the cheese to melt. You can also melt the cheese in the oven for a few minutes.

Serve the hot Au Jus in a small bowl with each sandwich for dipping.