1. Preheat your oven to 375°F (190°C).
2. In a large skillet, sauté onion and garlic over medium heat until softened, about 3 minutes. Add ground beef or lamb and cook until browned.
3. Stir in tomato paste, flour, Worcestershire sauce, and broth. Simmer for 5 minutes, stirring occasionally, until the mixture thickens. Add peas and carrots and mix well. Season with salt and pepper.
4. Transfer the meat mixture to a greased baking dish. Spread mashed potatoes evenly on top and fluff with a fork for texture. Dot with butter.
5. Bake for 20-25 minutes, or until the potatoes are golden and the filling is bubbling. Let cool slightly before serving.