Preheat the oven to 350°F / 176°C.
Don’t pull the rolls apart. Cut the loaf in half horizontally. Place the top halves aside. Optional: Toast the bottom half in the oven for 3-4 minutes, then remove from the oven.
Using a pan, turn the heat to medium (optional: add 2 tbsp oil). Add ground beef/chuck and cook for 5-6 minutes or until no longer pink. Optional: drain grease. Add salt, pepper, onion, garlic, paprika, Worcestershire sauce and mix. Remove meat and set aside.
Using the same pan. Add butter and turn up the heat to medium-high. Add sliced onions and cook for 5-6 minutes. Add sliced mushrooms and continue to cook for 5-6 minutes. Add salt, pepper, dried thyme, heavy whipping cream & Worcestershire sauce. Mix and cook for another 2 minutes. Remove the pan from heat source.
Evenly spread the cooked meat over the bottom half of the rolls. Then layer with mushroom mixture, cheese, and top halves of remaining rolls. Brush the melted butter over the tops of the rolls. Optional: sprinkle with white sesame seeds.
Cover with aluminum foil and bake for 30 minutes or until the cheese is melted.