Tip the dried mushrooms into a small heatproof bowl and cover with 250ml boiling water. Leave to soak for 20-30 mins until soft. Meanwhile, heat 2 tbsp of the oil in a large flameproof casserole dish over a medium-high heat and, once hot, stir in the beef and brown all over until deeply browned, about 10-12 mins. Remove to a bowl using a slotted spoon. Heat 1 tbsp of the remaining oil in the pan and cook the chestnut mushrooms for 8-10 mins until deeply browned, then remove to the bowl with the beef. Add the final 1 tbsp oil to the pan, reduce the heat to medium-low, and cook the onions, carrots and celery with a pinch of salt for 10-12 mins until starting to soften.

Drain the rehydrated mushrooms and roughly chop. Add to the onion mixture along with the garlic and tomato purée. Cook for 3-4 mins, then tip in the lentils, stock, butter and parmesan rind, if using. Bring to a simmer, then cover with a lid. Simmer over a low heat for 3 hrs until the beef is very tender and falls apart when pressed with the back of a spoon. Season to taste. Alternatively, you can cook in a pressure cooker on high pressure for 1 hr. Once cool, will keep in an airtight container in the fridge for up to five days, or in the freezer for up to three months.