Peel the onions and slice them thinly. Peel the carrots and dice them. Trim the roots and top 3cm off the leeks. Halve the leeks lengthways, and rinse well under a cold tap. Slice the leeks into chunky pieces. Slice the mushrooms thickly.

Peel the garlic cloves and crush or finely chop them. Finely grate the lemon zest.

Pour 1 tbsp oil into a large pan and warm over a medium heat. Slide in the chopped onions, carrots, mushrooms and leeks. Stir in the crushed garlic and lemon zest, and sprinkle in a pinch of salt and pepper. Fry for 10 mins, stirring occasionally, till the veg have softened and are glossy.

While the veg fry, scrub the potatoes and cut into small chunks. Drain and rinse the green lentils.

Add the bouquet garni to the pan. Tip in the potatoes and lentils. Crumble in the stock cube and spoon in 1 tbsp Dijon mustard. Pour in 1 ltr boiling water and stir well. Bring to the boil, then pop a lid on the pan and reduce to a gentle simmer. Cook for 30 mins, or till the potatoes are tender.

Meanwhile, separate the chard leaves and stalks. Roughly shred the leaves and finely slice the stalks. When the stew has cooked for 30 mins, stir in the chard. Cook for a further 5 mins. Squeeze in the juice from the lemon.

Have a taste of the stew and add more salt and pepper if needed. Ladle the stew into warm, deep bowls and serve.