Prep the ingredients. Slice the mushrooms, mince the garlic, and chop the shallot, parsley, and thyme. Grate the cheese if using. This cooks fast once you start.

Brown the beef. Heat a large skillet over medium-high. Add 1 tablespoon butter and the oil. Crumble in the ground beef, season with salt and pepper, and cook until well browned with crispy bits, about 6–8 minutes. Transfer to a plate, leaving drippings in the pan.

Sauté aromatics. Lower heat to medium. Add 1 tablespoon butter. Stir in the shallot and cook 1–2 minutes until softened. Add the garlic and cook 30 seconds, just until fragrant.

Cook the mushrooms. Add the mushrooms with a pinch of salt. Spread them out and let them sear, undisturbed, for 2 minutes. Stir and cook another 4–5 minutes until they release moisture and turn golden.

Build the pan sauce. Stir in thyme, Worcestershire, and red pepper flakes if using. Pour in the beef broth and lemon juice. Scrape up browned bits with a wooden spoon and let it simmer 2–3 minutes to reduce slightly.

Make it silky. Stir in the remaining 2 tablespoons butter. For a creamier finish, add heavy cream now. Simmer 1–2 minutes until glossy and slightly thickened.

Bring it together. Return the beef to the skillet. Toss to coat in the garlic butter sauce. Taste and adjust with more salt, pepper, or lemon for balance.

Add greens and cheese (optional). Fold in spinach or kale until just wilted, 30–60 seconds. Sprinkle Parmesan or Gruyère over the top and let it melt.

Finish and serve. Stir in parsley. Serve hot as is, or spoon over cauliflower rice, zucchini noodles, or a simple salad. Garnish with extra parsley and a crack of black pepper.