Prepare the Cauliflower Mash: Boil or steam the cauliflower until fork-tender (about 10–12 minutes). Drain and mash using a potato masher or blend until smooth. Add butter, heavy cream, salt, and pepper. Mix well and set aside.
Cook the Meat Filling: Heat olive oil in a skillet on medium heat. Add the onions and garlic, fry until softened. Mix this with the ground meat and also cook it until brown.
Season and Simmer: Add tomato paste, beef broth, thyme, rosemary, salt and pepper. Simmer for about 5–7 minutes, until it has thickened a little. Add optional veggies if using.
Layer the Pie: Preheat oven to 375°F (190°C). Dump the meat into a greased baking dish evenly. And, layer that with the cauliflower mash, and using a spatula even up.
Bake: Optional: Add shredded cheese. Uncovered, bake for 20 minutes or until the top is barely starting to brown.
Cool and Serve: Allow the pie to rest 5 minutes before slicing and serving.