Heat a large skillet over medium-high heat. Pat the beef dry with paper towels and season all sides with kosher salt.

Add the vegetable oil to the hot skillet and sear the roast for 1 to 2 minutes per side until it’s beautifully browned.

Transfer the beef to your slow cooker and sprinkle it lightly with ground black pepper.

In that same skillet, pour in the water, beef broth, and beef bouillon, scraping the bottom to lift any browned bits. Once dissolved, pour this mixture over the beef in the slow cooker.

Add the bay leaf, garlic, and sliced mushrooms around the roast. Sprinkle the onion soup mix on top, allowing some to fall into the liquid. Finish by adding the dried thyme and rosemary.

Cover the slow cooker and let it cook on LOW for 8 to 10 hours or on HIGH for 1 hour followed by 7 to 9 hours on LOW.

Once cooked, transfer the roast to a cutting board and let it rest for a few minutes before slicing thinly against the grain.

Preheat your broiler and place rolls cut-side up on a baking sheet. If desired, mix the softened butter with garlic powder and spread it lightly on the rolls, then broil until golden.

Flip briefly to crisp the outside, then return cut-side up and top with cheese. Broil just until melted.

Spread horseradish sauce on the melted cheese, add the sliced beef and mushrooms, and close the sandwiches.

Serve hot with small bowls of the cooking jus for dipping.