Heat 1 tablespoon of olive oil in a large saucepan over medium-high heat. Brown the beef mince in batches until deeply seared, then set aside.
Add the remaining 2 tablespoons of oil to the pan and stir in the chopped onions, carrots, and celery. Cook gently for about 20 minutes until the vegetables are soft and sweet-smelling.
Build a thick, glossy gravy
Stir in the chopped garlic, then sprinkle in the flour and add the tomato purée. Increase the heat and cook for a few minutes until the raw flour smell is gone and a paste forms.
Return the beef to the pan and pour in the red wine (or Guinness). Bring to a boil and reduce until the alcohol scent fades. Add the beef stock, Worcestershire sauce, thyme, and bay leaves.
Simmer until the filling coats the meat
Simmer the mixture uncovered for 45 minutes, stirring occasionally. If the sauce is still loose after 30 minutes, increase the heat slightly to thicken.
Once the sauce is thick and glossy, season well and remove the thyme stalks and bay leaves.
Mash, assemble, and bake
Boil the potatoes in salted water until tender. Drain well and let them steam-dry for a few minutes to ensure a fluffy texture.
Mash the potatoes until smooth, then stir in the milk, butter, and three-quarters of the cheddar cheese. Season with nutmeg, salt, and pepper.
Spoon the meat filling into ovenproof dishes. Pipe or spread the mash over the top, creating ridges with a fork. Sprinkle with the remaining cheese.
Bake at 220C (200C fan) for 25 to 30 minutes until the top is bubbling and golden. Let rest for a few minutes before serving.
Notes
Safety Tip: For a cottage pie that is truly heated through, aim for an internal temperature of 165°F (74°C) in the center.Pro Tip: Use a fork to rough up the mashed potato surface. The ridges create more surface area for crisp, golden peaks during baking.Storage Tip: You can assemble the pie and keep it in the refrigerator for up to 3 days or freeze it for up to 3 months. Thaw overnight before baking.Variation Tip: Ground turkey can be used as a lighter alternative, but ensure you reduce the gravy well and keep seasonings strong to maintain flavor depth.Nutrition information is estimated based on common ingredients and serving sizes and may vary.