01 - Preheat oven to 400°F. Scrub potatoes clean, poke several times with a fork, rub with olive oil, and season generously with salt. Place directly on oven rack and bake for 50-60 minutes until tender when pierced.
02 - While potatoes bake, heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add ground lamb and cook until browned, breaking up with a spoon as it cooks, approximately 7-8 minutes.
03 - Add diced onion, carrots, and minced garlic to the browned lamb. Sauté until vegetables are softened and onions are translucent, 5-7 minutes.
04 - Stir in tomato paste, Worcestershire sauce, dried thyme, and dried rosemary. Sprinkle flour or cornstarch over the mixture and cook for 1 minute, stirring constantly to eliminate raw flour taste.
05 - Pour in beef or vegetable stock and bring to a simmer. Cook until gravy thickens nicely, about 5 minutes. Stir in frozen peas and season with salt and pepper to taste. Remove from heat.
06 - Once baked potatoes are cool enough to handle, cut a lengthwise slit in each. Gently fluff the interior flesh with a fork, being careful not to tear the potato skins.
07 - Scoop out approximately one-third of the flesh from each potato, transferring to a mixing bowl. Keep the potato skins intact on the baking sheet.
08 - Spoon a generous amount of shepherd's pie filling into each prepared potato, packing lightly and mounding slightly above the skin.
09 - Add butter, milk or cream, shredded cheddar cheese, salt, and pepper to the reserved potato flesh. Mash until smooth and creamy, adjusting consistency with additional milk if needed.
10 - Spoon or pipe the mashed potato mixture over the filled potatoes, creating a decorative swirl if desired. Place potatoes on a baking sheet and broil for 3-5 minutes until topping is golden brown and lightly crisped.
11 - Remove from oven and sprinkle with freshly chopped parsley. Serve immediately while hot.