Sweet potato & spinach pithivier

A pithivier is a round pie, usually made by baking two discs of puff pastry with a filling enclosed between them. The pie should be slightly domed and is traditionally decorated with spiral lines drawn from the centre outwards with the point of a knife and with scalloping on the edge. We buy puff pastry rather than making it, which is a cheat but quicker!  

Serves 4-6

Prepare ahead Can be assembled up to 6 hours ahead and kept in the fridge.

200g (7oz) sweet potato, peeled and diced into 2cm (¾in) pieces

25g (1oz) butter

1 small leek, sliced

1 small onion, sliced

25g (1oz) plain flour, plus extra for dusting

250ml (9fl oz) hot milk

75g (3oz) spinach, coarsely chopped

1 tbsp grainy mustard

50g (2oz) mature Cheddar cheese, grated 320g (11oz) block of puff pastry

1 egg, beaten

salt and freshly ground

black pepper

• You will need a baking sheet lined with nonstick baking paper. Preheat the oven to 220C/ 200C fan/gas 7.

•  Cook the sweet potato in boiling salted water for about 8 minutes until just soft, then drain.

•  Melt the butter in a wide saucepan. Add the leek and onion then fry them gently for 5-7 minutes until soft. Add the flour and stir it in over the heat for a minute. Add the milk, a little at a time, stirring until the sauce has thickened. Add the spinach and stir until wilted. Stir in the mustard and cheese and season with salt and pepper, then add the cooked sweet potatoes. Transfer to a bowl, leave to cool, then chill in the fridge until cold.

•  Roll out the pastry on a floured surface until it is very thin. Cut out a 23cm (9in) circle and another that is slightly bigger.

•  Put the smaller circle on the lined baking sheet. Spoon the cold mixture into the centre, leaving a 2cm (¾in) border around the edge. Brush the edge with beaten egg. Place the larger circle on top and press the edges to seal. Crimp around the edges and make a small hole in the middle of the pie to let out steam. Starting from the centre, mark crescent-shaped lines, about 2cm (¾in) apart, down to the edge. Chill the pie in the fridge for 15 minutes if time allows.

•  Brush the pie with the remaining beaten egg and bake for 25-30 minutes until the pastry has puffed up, is cooked through and is crisp on top and underneath. Serve warm, with a dressed salad.