Preheat your oven to 400°F (200°C).
Peel and dice the gold potato, then place it in a pot of boiling water with the cauliflower florets; cook until both are very tender, about 12-15 minutes.
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 5 minutes until the onion is translucent.
Stir in the minced garlic and ground beef, breaking the meat apart with a spoon and cooking until browned.
Stir in the tomato paste, beef broth, frozen peas, and fresh thyme; simmer for 5 minutes until the sauce has thickened slightly.
Drain the cooked potato and cauliflower, then mash them together until smooth, seasoning with half of the sea salt and black pepper.
Spread the vegetable mash evenly over the beef mixture in the skillet, using a fork to create decorative ridges on top.
Bake for 15-20 minutes, or until the topping is golden brown and the edges are bubbling.
Remove from the oven and let rest for 5 minutes before serving.