Fill a large pan with water. Add a little salt, cover and bring to the boil. Slice the skin off the celeriac, then slice the roots off on a diagonal, leaving as much celeriac flesh behind as possible. Rinse and chop it into bite-sized chunks. Trim, peel and chop the parsnips. When the water is boiling, slide in the celeriac and parsnips. Simmer for 20 mins, till tender and crushable with a fork.

Meanwhile, peel the onion and finely chop it. Peel the garlic cloves and crush or finely chop them. Peel the carrot and finely chop it. Chop the vine tomatoes into small pieces. Pick the thyme leaves off their sprigs.

Pour 1 tbsp oil into a medium pan on a medium heat. Slide in the chopped onion, carrot and garlic. Add the thyme leaves and a pinch of salt and pepper. Fry for 5-6 mins, stirring occasionally. Fill your kettle and boil it.

Stir the soya mince into the veg. Drain and rinse the lentils. Shake dry and tip into the pan. Slide in the tomatoes. Crumble in the stock cube. Pour in 100ml boiling water and 1 tbsp Worcester sauce. Stir and bring to the boil. Reduce the heat to a simmer and cook the pie filling for 10 mins, stirring occasionally.

When the celeriac are parsnip are tender, drain them and give them a good mash.

Preheat your grill to medium-high. Pour the pie filling into an ovenproof dish and flatten to an even layer. Dollop the mash over the top and spread into an even layer.

Slide the pie under the grill and cook for 6-8 mins, till bubbling and a golden at the edges. Serve the pie straight away.