Cottage pie with celeriac mash

1. Preheat the oven to 220ºC, gas mark 7. Warm 1 tbsp oil in a large saucepan over a medium heat. Once hot, add the onion, carrot and celery and sauté for 4-5 minutes, then add the minced beef, increase the heat, and cook until browned. Mix in the garlic, tomato purée and 3 sprigs of thyme.

2. Add half the stock pot to the pan, along with 250ml just-boiled water and the Worcestershire sauce. Cover and simmer for 12 minutes. Mix 2 tsp cornflour with 1 tbsp cold water until smooth, then add this to the mince and cook for 3 minutes over a low heat, until slightly thickened.

3. Meanwhile, bring a large saucepan of water to the boil. Add the celeriac and boil for 10-15 minutes, until tender. Drain, then return to the pan and mash roughly with the milk and half the butter. Add the chopped rosemary and season. Transfer the mince to an ovenproof dish (remove the thyme stalks) then top with the celeriac mash. Dot the remaining butter on top, then bake for 20-25 minutes, until piping hot and golden.

4. Fry the red onion in the remaining oil with a pinch of salt, for 5 minutes. Add the brown sugar and cook for a further 5 minutes, until starting to caramelise. Add the remaining stock pot, 250ml just-boiled water and the remaining sprig of thyme. Mix the remaining 2 tsp cornflour with 1 tbsp cold water until smooth, then add to the pan and stir until thickened and simmering. Serve with the pie and seasonal green veg.