01 - Preheat the oven to 400°F.
02 - Bring a large pot of salted water to a boil. Add sweet potatoes and cook for 15–20 minutes until fork-tender. Drain and return to pot.
03 - Mash sweet potatoes with milk, butter, salt, and pepper until smooth. Set aside.
04 - Heat olive oil in a large skillet over medium heat. Sauté onion and garlic for 2–3 minutes until softened.
05 - Add carrots and celery; cook for 4–5 minutes until starting to soften.
06 - Add ground beef and cook, breaking it up with a spoon, until browned and cooked through.
07 - Stir in tomato paste, Worcestershire sauce, thyme, and rosemary. Mix well.
08 - Pour in beef broth, bring to a simmer, and cook for 8–10 minutes until slightly thickened. Stir in peas, season with salt and pepper.
09 - Transfer beef mixture to a large baking dish. Spread mashed sweet potatoes evenly on top.
10 - Bake for 20 minutes until the topping is lightly golden. For extra browning, broil for 2–3 minutes if desired.
11 - Let stand for 5 minutes before serving.