Preheat your oven to 200°C/Fan 180°C/Gas 6. Fill your kettle and boil it. Scrub the potatoes and chop them into bite-sized chunks. Tip them into a large roasting tin. Trim and scrub the carrots (no need to peel unless you want to), then thickly slice them on the diagonal. Trim the dry ends off the celery sticks and thickly slice the celery. Add the veg to the potatoes.

Nestle the boneless chicken thighs in the tin with the veg, skin-side up, and make sure everything is spread out in an even layer. Tuck most of the rosemary sprigs in the tin (keep a pinch of leaves back for garnishing).

Peel and crush the garlic and scrape it into a heatproof jug. Finely grate in the lemon zest and squeeze in the juice. Crumble in the stock cube and add 1 tbsp Dijon mustard. Add 500ml boiling water and stir to dissolve the stock cube and mix everything together.

Pour the flavoured stock into the roasting tin. Grind over a little black pepper. If your roasting tin has a lid, pop it on. Otherwise, cover the tin with a sheet of foil and crimp it to the edges to seal it. Slide the tin into the oven and roast for 20 mins.

After 20 mins, remove the lid or foil (being careful to protect your fingers from the steam). Return the tin to the oven and roast for a further 20 mins. While the chicken and the veg roast, toss the lamb’s lettuce with ½ tbsp olive oil and some salt and pepper.

The chicken should be browned and have cooked through (no pink in the meat if you slice into it) and the veg tender. They will have soaked up the flavours from the lemony stock. Serve the chicken and veg on warm plates with the lamb’s lettuce on the side.