Heat the large skillet over medium-high heat, add a splash of oil, then add the ground meat. Cook, breaking it apart with a spatula, until browned and fragrant, about 8-10 minutes.
Add chopped onions, diced carrots, and peas to the skillet. Stir well and cook until vegetables are tender and fragrant, about 5 minutes.
Sprinkle in thyme, rosemary, salt, and pepper. Stir to combine, letting the herbs release their aroma.
Pour in the gravy and stir well, allowing the mixture to simmer for a few minutes until slightly thickened and juicy.
Transfer the meat and vegetable mixture into a baking dish, spreading it evenly with a spatula.
Spoon the warm mashed potatoes over the filling, smoothing the top with the back of a spoon or spatula. If using, sprinkle shredded cheese evenly over the top.
Preheat your oven to 200°C (392°F). Place the assembled dish in the oven and bake for 20-25 minutes, until the top is golden brown and bubbling around the edges.
Remove from oven and let rest for about 5 minutes. This helps the layers set and makes serving easier.
Slice into portions, serve hot, and enjoy the comforting, crispy-topped shepherd’s pie with your favorite sides.