Heat the oil in a large skillet and add the ground beef. Continue cooking until it has browned all over, then drain any excess liquid.

Add the red bell pepper, celery, onion powder, tomato puree, thyme, Worcestershire sauce, beef broth, and bay leaves. Bring to a boil then reduce the heat and simmer for 20 minutes.

Meanwhile, preheat the oven to 400F.

Taste for seasoning and add salt and pepper as necessary. Remove (and discard) the bay leaves, then transfer the meat sauce into to a baking dish.

To make the topping, mash the cooked cauliflower with the milk and butter. Spoon the topping over the sauce. Note: For a smoother cauli mash you could run it through a food processor first.

Roast for 25-30 minutes until the sauce is bubbling and the topping is starting to brown.