Cook the cauliflower mash: Steam or boil the cauliflower florets until tender, about 10-12 minutes. Drain and mash with the heavy cream, butter, salt, and pepper. Blend until smooth and set aside.

Prepare the meat filling: In a large skillet, brown the ground beef or lamb over medium heat. Add the chopped onion, garlic, celery, and carrots. Cook for 5-7 minutes, until the vegetables are softened.

Add seasonings: Stir in the tomato paste, Worcestershire sauce (if using), and beef broth. Simmer for 5-10 minutes until the sauce thickens slightly. Add the fresh thyme, salt, and pepper.

Assemble the pie: Preheat the oven to 375°F (190°C). Spread the meat mixture evenly into the bottom of a baking dish. Top with the mashed cauliflower and smooth it out. Optionally, sprinkle shredded cheddar cheese on top.

Bake: Bake for 20-25 minutes, or until the top is lightly golden and the filling is bubbling.

Serve: Serve hot, and enjoy the keto-friendly version of this Irish classic.