Add the butter to a frying pan on a low heat and cook the onion and leek for 5 minutes until soft.
After 5 minutes, add the sweet potato, garlic and salt and pepper to taste. Cook for a further 5 minutes.
Crush the chestnuts using a fork, then add to the pan along with the spinach and fry for 2 more minutes, stirring occasionally.
Turn off the heat and sprinkle the feta over the mix. You can then combine the cheese with the rest of the mix.
Pour the mixture onto a piece of cling film, making a log shape out of it.
Wrap it tightly and refrigerate for 1 hour.
Preheat the oven to 180 degrees celsius and lay the sheet of puff pastry on a baking tray.
Roll the filling into the middle of the pastry, then using a splash of water, fold the edges together. Use a fork to squish the ends together and remove any excess pastry.
Bake for 35 minutes and serve.
300g puff pastry
½ leek, peeled and chopped
½ onion, diced
½ sweet potato peeled and chopped
130g chestnuts, cooked and peeled
1 tbsp butter
1 clove garlic, crushed
75g feta cheese