Prep Beef: Place chuck roast on a large plate. In a small bowl combine 1 tablespoon salt, 2 teaspoons onion powder, 2 teaspoons garlic powder, & 1/2 teaspoon ground black pepper; stir to combine. Pat chuck roast dry with a clean paper towel and cover in the seasoning ensuring it is fully coated. Set aside. 

Slow Cooker Ingredients: Add 4 cups beef broth, french onion soup mix, sliced onions, 1 tablespoon minced garlic, 2-3 sprigs fresh thyme, 3 teaspoons worcestershire sauce, 1 teaspoon liquid smoke and 1 teaspoon dijon mustard to the slow cooker. Scoop out 1/4 cup of the broth mixture and set next to the stove. 

Sear Beef: Bring a large cast iron skillet to medium-high heat. Add two tablespoons butter and let melt. Sear chuck roast on all sides. Transfer to slow cooker. 

Deglaze the Pan: Add the 1/4 cup beef broth to the hot skillet and scrape up all the bits that are sticking to the pan. Add the remaining two tablespoons of butter and let melt. Once the bottom of the pan is scraped clean, transfer the liquid to the slow cooker and pour over the top of the chuck roast. 

Let it Cook: Cover the slow cooker and cook on HIGH 4 hours or LOW 8 hours. Shred the beef with two forks before serving. 

Assemble Sandwiches: Butter the inside of each hoagie bun, add desired amount of onions and shredded beef, add cheese on top (and a little horseradish mayo, if desired).

Serve: Enjoy each sandwich with a small bowl of broth (or au jus) from the slow cooker for dipping.