01 - Preheat oven to 400°F.
02 - Place sweet potatoes in a large saucepan, cover with water, and bring to a boil. Simmer for 15–20 minutes until tender.
03 - While the sweet potatoes cook, heat olive oil in a large skillet over medium heat. Add onion and carrot; sauté for 5 minutes until softened.
04 - Add garlic and mushrooms; cook for another 3–4 minutes until the mushrooms release their juices.
05 - Add ground beef, breaking it up with a spoon, and cook until browned.
06 - Stir in tomato paste, diced tomatoes, Worcestershire sauce, thyme, rosemary, salt, and pepper. Pour in beef stock and mix well. Simmer uncovered for 15 minutes, stirring occasionally, until thickened.
07 - Drain the sweet potatoes and mash with butter, milk, salt, and pepper until smooth and creamy.
08 - Spoon the beef filling into a baking dish (about 9x9 in). Spread the sweet potato mash evenly on top.
09 - Bake for 20–25 minutes until the top is slightly golden and the filling is bubbling.
10 - Let rest for 10 minutes before serving.