Preheat the oven: Preheat your oven to 375°F (190°C).

Brown the beef: In a large skillet, heat the butter or olive oil over medium heat. Add the ground beef (or beef stew meat) and cook until browned, about 5-7 minutes. Season with salt, pepper, and smoked paprika. Remove the beef from the skillet and set aside.

Sauté the onions and mushrooms: In the same skillet, add the chopped onions, garlic, and sliced mushrooms. Cook for 4-5 minutes until the vegetables are softened and the mushrooms have released their moisture.

Make the creamy sauce: Stir in the beef broth, heavy cream, and fresh thyme or rosemary. Let the mixture simmer for 5-7 minutes, allowing the sauce to thicken slightly. Stir in the grated Parmesan cheese and adjust seasoning with salt and pepper.

Assemble the casserole: In a baking dish, combine the cooked beef with the creamy mushroom sauce. If desired, top with shredded cheddar cheese for an extra cheesy finish.

Bake: Bake in the preheated oven for 15-20 minutes, or until the casserole is bubbly and the cheese is melted and golden.

Serve: Garnish with freshly chopped parsley and serve hot. This casserole pairs wonderfully with cauliflower mash or a simple green salad for a complete keto meal.