Make the puff pastry: Add the flour and a pinch of salt to a large mixing bowl, then add the butter. Rub the flour and butter between your fingers to start breaking it up. Instead of doing this until it resembles fine crumbs like you would with shortcrust, stop before it’s fully broken down. You want to still be able to see large flecks of butter in the flour.

Add the water, little by little and mixing gently with your hands each time, using enough water to bring the dough together into a soft ball but not so much that it becomes too sticky to handle. Lightly flour a clean work surface and rolling pin, then roll out the dough away from you into a rectangle (roughly 30 × 20 cm/12 × 8 in), with the short edge nearest to you. At this point, you should be able to see the flecks of butter in the dough. It will be quite sticky, so don’t be afraid to keep dusting your surface and rolling pin with more flour.

Next, fold the dough – take the top third and bring it down towards the centre, then fold the bottom third over it. Turn the dough 90 degrees (a quarter turn) so that the new short edge is nearest to you. Roll out to a rectangle again and fold, just as you did before, sprinkling with flour if the dough becomes sticky. Repeat once more, so you have rolled and folded the dough three times. After the last fold, instead of turning it, fold it in half again (short end to short end), and transfer to a plate.

Cover and place in the refrigerator for 30 minutes to chill before rolling out to use.

While the pastry is chilling, prepare the filling. Heat a small frying pan over medium heat. Add the olive oil and chopped leek and fry for 5 minutes until soft. Remove from the heat.

Place all the filling ingredients into a large bowl, then use your hands to mix them together, squeezing the ingredients into the pork. Season well with salt and pepper and set aside.

Roll out the pastry on a lightly floured surface to a large rectangle, about 60 × 20 cm (24 × 8 in) and 3–5 mm (⅛– ¼ in) thick. If it’s difficult to roll out in one piece, you can roll two smaller rectangles, then dab the edges with a little water and press them together to create one large sheet.

Using your hands, place the pork filling lengthways down the centre of the pastry, pressing it firmly into a long sausage shape. Lift one long edge of the pastry and fold it over the filling. Lightly brush the opposite edge with water, then fold it over so it overlaps the first edge. Press gently to seal. Finally, roll the whole pastry cylinder over so the seam is underneath. Bring the two ends of the cylinder together to create a circular wreath shape, dabbing a little water on the pastry ends before pressing them together to seal – don’t worry if it’s not perfect! Carefully transfer the wreath to a large baking tray lined with baking paper, cover and chill in the refrigerator for 30 minutes.

Preheat the oven to 200ºC (180ºC fan-forced/400°F). Remove the wreath from the refrigerator. Using a sharp knife, make 8 cuts into the pastry and sausage meat as if you were slicing it into eighths, but cut only halfway through the sausage. To finish, brush the pastry with the beaten egg, score the top of the pastry if you would like, and sprinkle with sesame seeds. Bake for 45 minutes–1 hour or until the pastry is golden brown and flaky and the sausage meat is cooked through. Allow to cool for 15 minutes before slicing it up to serve.