Cottage Pie Filling

1. Heat the olive oil over medium heat in a large, deep pan. Add the onion and garlic. Cook, stirring, for 1 minute until slightly softened.
2. Add the celery, carrot and zucchini. Cook, stirring, for 3–4 minutes, until softened.
3. Increase the heat to high, add the beef and cook for 4–5 minutes or until starting to brown.
4. Stir in the flour, followed by the tomato paste.
5. Add the beef stock, bay leaves, thyme, Worcestershire sauce, pepper and salt. Bring to a simmer, then reduce the heat to medium–low so that the sauce is just simmering.
6. Cover and cook for 10 minutes. Uncover and cook for a further 20 minutes, stirring regularly. The sauce will thicken into a lovely gravy (see note 2).
7. Set the filling aside to cool.

Mashed Potato Topping

1. Bring a large pot of salted water to the boil (you will need a pot large enough so that the potatoes are covered by at least 5 cm/2 inches of water).
2. Add the peeled, quartered potatoes to the water and cook for 15–20 minutes until soft enough to pierce with a fork.
3. Remove the pot from the heat. Drain the potatoes using a colander and place the potatoes back in the pot. Allow them to steam-dry for 1–2 minutes. This removes any excess water.
4. Add the butter and mash the potatoes twice around the pot before adding the milk. Continue to mash until smooth and fluffy, and season with the salt.

Assemble Pie

1. Preheat the oven to 200°C (400°F) (180°C/350°F fan-forced).
2. Once the beef mixture has cooled slightly, transfer it into a large baking dish (approximately 30 x 25 cm/12 x 10 inches). You can skip this step if you have made your filling in an oven-safe pan. 
3. Spoon the mashed potato on top of the beef mixture and use the back of a spoon to spread it out evenly. Do this while the mashed potato is hot, as it’s much easier to spread. Use a fork to rough up the surface gently.
4. Sprinkle with parmesan. Bake for 30 minutes or until the topping is golden and crispy.