Fill and boil your kettle. Tip the porcini mushrooms into a heatproof bowl. Pour over enough boiling water to cover them and let them soak for 5 mins, then drain them and rinse under cold water. Pop them back in the bowl and pour in 200ml hot water from the kettle and set aside.

While the porcini mushrooms soak, trim the roots and top 3cm off the leek, then halve it and rinse out any grit. Finely slice the leek. Trim the dry ends off the celery stalks and finely slice them. Peel and slice the carrots into 1cm-thick chunks.

Heat 2 tsp olive oil in a large pan on a medium heat. Add the leek, celery and carrots. Season with a pinch of salt and pepper and cook, stirring, for 5 mins. Fill and boil the kettle again.

While the veg fry, thickly slice the chestnut mushrooms, leaving any smaller ones whole. Peel and thinly slice 1 garlic clove. After 5 mins cooking, add the chestnut mushrooms and garlic to the pan. Cook for 5 mins, stirring often, till the mushrooms are juicy. Pour in the porcini and their soaking liquid. Let the mixture bubble up.

Tip in the chopped tomatoes. Cover and simmer for 15 mins. While the bourguignon is simmering, tip the pearl barley into a small pan. Cover the barley with hot water from the kettle. Cover and simmer over a medium heat for 15-20 mins.

While the mushrooms and barley cook, peel and grate or crush the remaining garlic clove. Finely chop the parsley stalks and leaves. Zest and juice the lemon (or 1 half if your lemon is on the large side) Whisk everything together in a small bowl with 1 tbsp each cold water and olive oil. Season. This is your sauce verte.

When the barley is tender, drain it. Taste the bourguignon and adjust the seasoning if needed. Serve in warm bowls with the barley, and the sauce verte drizzled on top.