In a slow cooker, combine 2 pounds of beef chuck, 2 sliced medium onions, 2 cups of beef stock, 2 teaspoons of garlic salt, 1 teaspoon of black pepper, and 1 packet of Lipton onion soup mix. Cover and cook on high for 5-6 hours until the beef is incredibly tender and easily shreds with a fork.

Once your pot roast has finished cooking, carefully remove the beef from the slow cooker and place it on a cutting board. Shred the meat using two forks until it's in bite-sized pieces, then set aside along with the caramelized onions.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add the sliced onions and a pinch of salt, cooking slowly for about 5 minutes until they turn a lovely golden brown. Stir in the reserved onions from the slow cooker along with a splash of the beef stock, reducing the mixture for an additional 2-3 minutes until it thickens slightly.

Heat another skillet over medium heat and melt the remaining 2 tablespoons of butter. Butter one side of four slices of crusty bread, then layer the unbuttered side with a slice of Swiss cheese. Top with a generous portion of the shredded pot roast and caramelized onions, then sprinkle with 8 ounces of shredded Gruyere cheese. Place a second slice of bread, buttered side facing up, over the fillings to create the sandwich.

Carefully transfer the assembled sandwiches to the heated skillet. Grill for about 3-4 minutes on one side, or until the bottom is golden brown and crispy. Gently flip the sandwiches over and continue to grill until the other side is browned and the cheeses have melted, which should take an additional 3-4 minutes.

Slice the sandwiches in half, revealing the gooey interior, and serve warm to enjoy your Rustic Pot Roast French Onion Grilled Cheese Sandwich!