Peel the onion and carrots. Blitz coarsely along with the celery and garlic in a food processor. Remove from the processor and repeat with the mushrooms. If you don't have a food processor you can finely chop it all, but do not be tempted to grate it!
Heat 2 tbsp oil in a large saucepan over a medium heat and add the blitzed onion, carrot, garlic and celery. Add a big pinch of salt and cook for 10 mins until completely softened. Add the tomato purée and cook for 2 mins before tipping in the mushrooms. Cook for 5 mins until softened.
Add the drained lentils, tinned tomatoes, miso, and stock, then simmer for 30-40 mins until reduced. Season with salt and pepper.
