Sweet Potato and Parsnip Gratin

Heat a drizzle of oil in a large frying pan on medium-high heat. When hot, add the red onion and cook until soft and jammy, 8-10 mins, stirring regularly. TIP: Lower the heat if they are browning too quickly. Once softened, stir in the garlic and thyme. Pour in the water (see ingredients for amount) and the vegetable stock powder. Stir to dissolve and reduce the heat to low.

Peel and thinly slice the sweet potato into 1cm thick slices. Trim the parsnip, peel and thinly slice into 1cm thick slices as well. Once the water is boiling, pop the veggies and a good pinch of salt into the pan and boil until tender, 10-12 mins. TIP: The veg are cooked when you can easily slip a knife through them. Add the cavolo nero to the pan 3 mins before the end of the cooking time. Once cooked, drain all the veggies into a colander.

Stir the creme fraiche and half the mustard into the onion mixture, then remove from the heat. Carefully add the cooked root veg into the pan, add a pinch of salt and pepper and mix gently to combine. Add a splash of water if the mixture is a little dry. Transfer everything into an ovenproof dish and sprinkle with the cheesy panko breadcrumbs. Bake on the top shelf of your oven, until the topping is golden, 8-10 mins.

In the meantime, mix the remaining mustard and a drizzle of oil together in large bowl. Add the rocket and toss to lightly coat the leaves in the dressing.