Preheat the oven to 400°F (200°C). Rub the potatoes with olive oil, prick them with a fork, and bake directly on the oven rack for 50-60 minutes until tender.
Slightly, slice off the top third of each potato. Scoop out most of the insides, leaving a thin layer for structure. Place the scooped-out potato in a bowl.
Mash the potato flesh with butter, milk (or cream), salt, and pepper until smooth. Set aside.
Brown the ground lamb or beef, then drain any excess grease.
Add the onion, garlic, and carrots to the skillet and cook for 3-4 minutes until softened.
Pour in the red wine and let it cook for 2-3 minutes until reduced by half.
Add the beef broth, Worcestershire sauce, Maggi Seasoning (if using), thyme, salt, and black pepper. Let it simmer for 5 minutes until it thickens slightly. Stir in the cornstarch-water mixture and cook for another 2 minutes. Add the peas and remove from heat.
Fill each potato shell with the meat mixture, then top with the mashed potatoes. Smooth or pipe the topping and sprinkle with cheddar cheese if using.
Return the stuffed potatoes to the oven and bake for 15-20 minutes until the tops are golden and slightly crisp.
Serve hot and enjoy!