1

Mist a deep ovenproof pan or flameproof casserole with cooking spray and set over a medium-high heat. Add the chicken and cook until browned all over. Transfer to a plate and set aside.

2

Combine the cornflour and 2 tbsp of the stock to make a smooth paste. Add the remaining stock to the pan with the wine and most of the herbs and bring to the boil, scraping the bottom of the pan to incorporate any of the caramelised pan juices. Stir in the cornflour paste then add the mustard, leeks, celeriac and chopped sweet potatoes. Simmer over a low heat for 5 minutes. Return the chicken to the pan and simmer for 8-10 minutes, until the sauce has thickened.

3

Preheat the oven to 200ºC, fan 180ºC, gas mark 6. Layer the slices of sweet potato over the top of the stew, overlapping as you go, until the stew is completely covered. Brush the potato topping with the oil and scatter over the remaining herbs. Season and bake for 25-35 minutes, until the top is golden and the potato is cooked through.