Preheat and prep: Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish. Thaw the hash browns if still frozen and pat them dry to remove excess moisture.

Brown the beef: Warm a large skillet over medium-high heat. Add the ground beef, season with salt and pepper, and cook until browned, breaking it up with a spoon, about 6–8 minutes. Drain off any excess fat if needed.

Sauté aromatics: Add the chopped onion to the skillet and cook until softened, 3–4 minutes. Stir in the garlic and cook 30 seconds, just until fragrant.

Season the filling: Stir in Worcestershire sauce, paprika, and thyme. If using mushrooms or peppers, add them now and cook until tender. Taste and adjust salt and pepper.

Make it creamy: Reduce heat to medium-low. Add the condensed soup, sour cream, and 1/2 cup beef broth or water. Stir until smooth and heated through. Fold in 1 cup of the shredded cheese until melted. If using peas or mixed vegetables, add them now.

Combine with hash browns: In a large bowl, mix the thawed hash browns with the beef mixture until evenly coated. If it looks too dry, splash in a bit more broth. You want it creamy but not soupy.

Assemble the casserole: Spread the mixture evenly in the prepared baking dish. Sprinkle the remaining 1 cup of cheese over the top.

Optional crunchy topping: Toss crushed cornflakes or cracker crumbs with the melted butter and a pinch of paprika. Scatter over the cheese for extra texture.

Bake: Place on the middle rack and bake for 30–40 minutes, until the edges are bubbling and the top is golden and crisp. If the top browns too quickly, tent loosely with foil.

Rest and serve: Let the casserole rest for 10 minutes before slicing. Garnish with chopped green onions or parsley if you like. Serve hot.