Preheat your oven to 400°F (200°C).
Place the peeled, cubed potatoes and cauliflower florets in a pot of boiling water and cook for 12-15 minutes until very tender.
While the vegetables boil, heat the olive oil in a large oven-safe skillet over medium heat.
Add the diced onion and carrots to the skillet, sautéing for about 5 minutes until they begin to soften.
Add the grass-fed ground beef to the skillet, breaking it apart with a wooden spoon and browning it thoroughly.
Stir in the minced garlic, tomato paste, dried thyme, sea salt, and black pepper, cooking for another 60 seconds until fragrant.
Pour in the beef bone broth and add the frozen peas, simmering for 3-4 minutes until the liquid has reduced and thickened into a light gravy.
Drain the potatoes and cauliflower, then mash them together using a potato masher or fork until smooth and creamy.
Spread the potato-cauliflower mash evenly over the beef and vegetable mixture in the skillet.
Place the skillet in the oven and bake for 15-20 minutes until the topping is lightly golden and the filling is bubbling.