Preheat your oven to 375°F (190°C). Prepare the stuffing mix according to the package directions and set it aside.
In a large skillet over medium heat, melt the butter. Add the chopped mushrooms and onion and cook until softened, about 10 minutes. Remove 2 tablespoons of the cooked vegetables and stir them into the prepared stuffing.
In a small bowl, combine the torn bread and 1 cup of milk. Let it soak for 5 minutes until the bread is saturated.
In a large bowl, add the ground beef, the soaked bread mixture, beaten eggs, dried sage, salt, pepper, and the remaining sautéed mushrooms and onions. Gently mix with your hands until just combined. Avoid overmixing.
Lay a large piece of plastic wrap on your counter. Pat half of the meat mixture into an 8x12-inch rectangle on the plastic. Spread the stuffing mixture evenly over the meat, leaving a small border. Top with the remaining meat mixture and pat it down to cover the stuffing.
Using the plastic wrap to help, carefully roll the meatloaf from the short end into a tight log. Pinch the seams to seal. Place the meatloaf, seam-side down, in a 9x13-inch or similar large baking dish.
In a medium bowl, whisk together both cans of soup, 1/3 cup of milk, and the Worcestershire sauce. Pour this topping evenly over the meatloaf.
Cover the dish tightly with foil. Bake for 1 hour and 30 minutes, or until the center of the meatloaf registers 160°F (71°C) on an instant-read thermometer.
Let the meatloaf rest for 10 minutes before slicing. Carefully drain any excess grease from the pan and spoon the gravy over the slices to serve.