01 - Preheat oven to 400°F.
02 - Place potatoes and whole garlic cloves in a large pot. Cover with cold, salted water and bring to a boil. Simmer until potatoes are 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 if desired.
04 - While potatoes cook, 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 if thickening is desired.
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.