Preheat your oven to 200°C (390°F).
Heat a large skillet over medium heat and add a splash of oil. Once hot, add chopped onions and diced carrots, sautéing until fragrant and slightly caramelized, about 8 minutes. You'll notice the vegetables soften and develop a sweet aroma.
Add the ground meat to the skillet, breaking it apart with a spatula. Cook until browned and cooked through, about 10 minutes. Stir occasionally to get an even sear and listen for the sizzle and slight caramelization.
Stir in the frozen peas and thyme, cooking for another 2–3 minutes until the peas are heated through. Season with salt and pepper to taste. The mixture should be thick and flavorful, with a rich aroma filling the kitchen.
Meanwhile, place the peeled and chopped potatoes into a large pot of salted boiling water. Cook until tender, about 15 minutes, until they easily mash when pierced with a fork.
Drain the potatoes well and return them to the hot pot. Add butter and warm milk, then mash until smooth and fluffy. Taste and adjust with salt and pepper as needed. The mash should be creamy and inviting, with a silky texture.
Spread the meat and vegetable mixture evenly into a baking dish. Use a spatula to smooth the surface and create slight ridges for extra crispiness.
Dollop the mashed potatoes over the filling, then spread evenly with a spatula or fork. Use the back of a fork to create peaks and ridges on top, which will crisp up nicely during baking.
If desired, sprinkle shredded cheddar cheese evenly over the top for a golden, crispy crust. Place the dish in the oven and bake for 20–25 minutes, until the top is golden brown and bubbling around the edges.
Remove from the oven and let rest for 5 minutes. This helps the filling set, making it easier to serve clean slices and ensuring the flavors meld beautifully.
Serve hot, garnished with fresh herbs if desired, and enjoy the crispy, hearty layers of your cozy shepherd’s pie.
