In a large skillet over medium heat, melt butter. Add diced mushrooms.
Cook for a few minutes. Add mushrooms.
When the skillet gets dry, add the 1/2 cup of beef broth. Cook until mushrooms are almost cooked.
Remove from skillet to a plate. Add meat to the skillet. Season with the salt, pepper, and garlic powder.
Spread meat out into an even layer and brown. When one side has browned, flip and brown the other size. This happens very fast.
Remove the meat to the plate with the onion and mushrooms.
Leave any liquid in the skillet. Add the remaining beef broth and Montreal steak seasoning.
When hot, add the heavy cream.
Stir, allow to cook for a minute or two.
Add the meat, mushrooms, and onions back to the skillet. Stir, coat everything, and heat through. Serve on top of mashed cauliflower.