01 - Heat the oven to 400°F.
02 - Place peeled and cubed sweet potatoes in a large pot, cover with cold water, add a pinch of salt, bring to a boil, then simmer for 15 to 20 minutes until tender.
03 - Drain sweet potatoes and mash with butter, milk, salt, and pepper until smooth. Set aside.
04 - Heat olive oil in a large skillet over medium heat; cook chopped onion for 2 to 3 minutes until softened.
05 - Stir in minced garlic and diced carrots, cooking for an additional 3 minutes.
06 - Add ground beef, break apart with a spoon, and cook for 5 to 7 minutes until browned.
07 - Mix in tomato paste, Worcestershire sauce, thyme, and rosemary, cooking for 2 minutes to blend flavors.
08 - Pour in beef broth, bring to a simmer, and cook for 5 minutes until slightly thickened.
09 - Stir frozen peas into the filling and adjust seasoning with salt and pepper. Remove from heat.
10 - Transfer the beef mixture to a 2-quart baking dish and evenly spread the sweet potato mash on top.
11 - Use a fork to make ridges in the sweet potato mash for a crispy texture.
12 - Bake uncovered for 20 to 25 minutes until the top is golden and the filling is bubbling.
13 - Allow the dish to rest for 5 minutes before serving.