Ingredients

· 375g pack ready-rolled, all-butter shortcrust pastry

· 750g sweet potato (about 3 long and large), peeled

· 3tbsp olive oil

· Salt and pepper to taste

· 5 thyme sprigs

· 50g Parmesan cheese, finely grated

· 2 eggs

· 3tbsp crème fraîche

· Salad leaves, to serve (optional)

Method

Use the pastry to line a 23cm diameter tart tin with a removable base, patching as needed and leaving the excess pastry untrimmed. Chill for 20 minutes. Meanwhile, preheat the oven to 170°C. Prick the pastry base several times with a fork and line with baking paper. Fill the centre with baking beans or uncooked rice to weigh the paper down. Set on a baking tray and cook for 15 minutes until the pastry no longer looks raw. Remove the paper and beans, and return the pastry case to the oven for five more minutes or until it turns a pale golden colour. Trim off the excess pastry flush with the top of the tin and set aside. Reduce the oven to 150°C. For the sweet potatoes, to create long ribbons, it is best to slice them from top to bottom with a mandolin, using a hand guard, but a sturdy swivel peeler also works well. The slices must be long, very thin and bendy. Put the potato slices in a mixing bowl and toss with two tablespoons of the olive oil to coat and a little salt and pepper.

Strip the thyme leaves from two of the stalks and combine with the grated Parmesan, eggs and crème fraîche in a small bowl. Season lightly then spread this mixture over the base of the tart and top with the sweet potato, arranged vertically in a concentric circle from the outside to the inside. The potato slices should begin to form a rose effect. Scatter with the remaining thyme sprigs and drizzle with the remaining olive oil. Bake for 40 minutes or so, until the sweet potato is tender. Serve warm or at room temperature, with salad leaves.