This veggie traybake is satisfying enough to eat by itself as a main or try it alongside your Sunday roast.
- Prepare15 mins
- Cook45 mins
- Total time1 hr
Preheat the oven to 220oC, gas mark 7. Thinly slice the potatoes (to a thickness of about 0.3cm) and put in a very large saucepan or casserole dish. Cover with cold water, bring to the boil, then simmer for 5 minutes. Drain in a colander and set aside.
Return the pan to a medium heat with the oil. Add the leeks, garlic and a pinch of salt, and sweat until soft (about 5 minutes). Strip the cavolo nero leaves from the stalks and roughly tear. Add to the pan with the thyme, and sweat for another 3-4 minutes. Add both creams and the milk to the pan and bring gently to a simmer. Stir in the mustard and about 3⁄4 of the cheese; season.
Carefully tip the potatoes into the pan and turn in the sauce. Transfer everything to a 1.5-litre baking tray. Scatter over the remaining cheese and some extra thyme sprigs, and bake for 25 minutes until golden and bubbling. Stand for 5 minutes before serving with a green salad, if liked.
Charlotte potatoes are a waxy variety that hold their shape well in this gratin. Their thin papery skins mean you don't need to peel them.
And to drink...
Marquis de Chasse, Bordeaux, France (75cl), is a beautifully smooth blend of Merlot and Cabernet Sauvignon that pairs well with this dish.