Bring a large pot of water to a boil and add a generous pinch of Salt. Peel and cut the Floury Potatoes into even chunks, then boil until very tender, about 15–20 minutes.
Meanwhile, heat a tablespoon of Vegetable Oil in a large frying pan over medium heat. Add a finely chopped Onion, diced Carrot and chopped Celery and cook until softened, 6–8 minutes.
Turn the heat up slightly and add the Beef Mince, breaking it up with a spoon; brown thoroughly until no pink remains.
Stir in a tablespoon of Plain Flour and cook for 1 minute to remove the raw flour taste and help thicken the sauce.
Mix in a couple of tablespoons of Tomato Paste and a splash of Worcestershire Sauce, then pour in about 300–400 ml of Beef Stock. Add a few sprigs of Thyme and a Bay Leaf, bring to a simmer and cook until the sauce is reduced and glossy, about 10–15 minutes. Season with Black Pepper and more salt if needed.
Remove and discard the bay leaf and any woody thyme stems, then taste and adjust seasoning.
Drain the potatoes and return them to the pot; mash with a knob of Butter and a splash of Milk until smooth and fluffy. Season the mash with salt and pepper to taste.
Spoon the meat mixture into a suitably sized baking dish and spread evenly. Dollop or pipe the mashed potatoes over the top, smoothing or creating peaks with a fork for crisped edges.
Bake in a preheated oven at 200°C (400°F) for 20–25 minutes, until the top is golden and the filling is bubbling; for extra color, finish under the grill for 2–3 minutes.
Let the pie rest for 5–10 minutes before serving so the layers set — then serve hot and enjoy.
