01 - Preheat oven to 400°F for baking the assembled pie.
02 - Place potatoes and whole garlic cloves in a large pot. Cover with cold, salted water and bring to a boil. Simmer until fork-tender, about 15–20 minutes. Drain well.
03 - Return potatoes and garlic to the pot. Add butter, warm milk, and cream. Mash until smooth and creamy. Season with salt and pepper. Stir in chopped chives or parsley.
04 - Heat olive oil in a large skillet over medium heat. Add onion, carrots, and celery; sauté for 5–7 minutes until softened.
05 - Add ground lamb or beef to the skillet. Cook, breaking it up with a spoon, until browned, about 5 minutes. Drain excess fat if needed.
06 - Stir in minced garlic and tomato paste; cook for 1 minute. Sprinkle flour over meat and vegetables, stir, and cook for another minute to thicken.
07 - Add peas, broth, Worcestershire sauce, thyme, rosemary, salt, and pepper. Simmer for 5–7 minutes, until slightly thickened.
08 - Spread the meat filling evenly in a 9x13 inch baking dish. Top with creamy garlic mashed potatoes, smoothing with a spatula. Create swirls for crispier edges if desired.
09 - Bake uncovered for 25–30 minutes, or until the top is golden and filling is bubbling. Broil for 2–3 minutes for extra color.
10 - Let rest for 10 minutes before serving to allow the pie to set.