Prepare the Potatoes: Place the peeled and diced potatoes in a pot of salted water. Bring to a boil and cook until tender, about 15-20 minutes. Drain and set aside.
Cook the Meat: In a large skillet over medium heat, add the ground beef or lamb. Cook until browned, breaking it apart with a spoon as it cooks. Drain any excess fat.
Add Aromatics: Add the chopped onion and minced garlic to the skillet with the meat. Sauté until the onion becomes translucent, about 5 minutes.
Incorporate Vegetables: Stir in the mixed vegetables, tomato paste, Worcestershire sauce, thyme, rosemary, and season with salt and pepper. Cook for another 5 minutes, ensuring everything is well combined and heated through.
Mash the Potatoes: Return the drained potatoes to the pot. Add milk and butter, and mash until creamy. Season with salt and pepper for additional flavor.
Assemble the Pie: Preheat the oven to 400°F (200°C). In a baking dish, spread the meat and vegetable mixture evenly. Top with the mashed potatoes, spreading it out evenly over the surface.
Add Cheese (Optional): If using, sprinkle shredded cheddar cheese on top of the mashed potatoes for a cheesy crust.
Bake: Bake in the preheated oven for about 20-25 minutes, or until the top is golden and crispy.
Serve: Let cool slightly before serving. Scoop out portions to serve.
Notes
Feel free to customize the vegetables based on your preference.