Heat olive oil in a skillet over medium heat and cook onion until softened.
Add garlic briefly, then add ground beef and brown fully.
Stir in tomato paste, Worcestershire sauce, thyme, salt, and pepper.
Add beef broth and simmer until thickened.
Steam or boil cauliflower until very tender.
Drain well and blend with butter, heavy cream, and salt until smooth.
Spread the beef mixture in a baking dish.
Add the cauliflower mash on top and smooth evenly.
Bake at 400°F for 18–22 minutes until set and lightly browned.
Let rest 5 minutes before serving.