Potato, leek and stilton pithivier

Method

1. Complete step 1 as in the master recipe to prepare the pastry discs.
2. For the filling, bring a large pan of salted water to the boil. Add the sliced potatoes, bring back to the boil, then cook for 2 minutes or until just tender when pierced with the tip of a knife. Drain well.
3. Melt the butter in a medium pan, add the shallots and cook gently for 3-4 minutes until softened. Add the leeks and thyme, then cook, uncovered, for 8 minutes until the leeks have softened. Season with salt and pepper to taste, transfer to a mixing bowl and leave to cool.
4. Beat the egg with the crème fraîche, garlic and mustard, season with salt and pepper, then stir into the cooled leek mixture.
5. Remove the pastry discs from the fridge. Layer the sliced potatoes in the centre of the smaller disc, leaving a 2.5cm border around the edge and seasoning with pepper and a little salt as you go (the stilton will add saltiness). Scatter the crumbled stilton over then, using a slotted spoon, top with the leek mix. Discard any runny egg left in the bowl.
6. Beat the egg yolk with 1 tsp cold water, then brush a little over the pastry border. Lay the second disc over the filling and finish assembling the pithivier as in step 4 of the master recipe, pressing the edges together to seal and smoothing out any air as you go. Mark the border with a fork, then make a small hole in the centre to allow the steam to escape. Chill for 20 minutes.
7. Meanwhile, heat the oven to 220°C/200°C fan/gas 7. Remove the pithivier from the fridge and brush with the rest of the egg glaze. Press into the edges of the pastry again with a fork to make sure it’s fully sealed.
8. Bake for 15-20 minutes until puffed and golden. Turn down the oven to 180°C/160°C fan/gas 4, then bake for 40 minutes more or until the pastry is deeply golden. If it starts to brown too quickly, lay a sheet of foil loosely over the top. Transfer to a cooling rack to cool slightly. Serve warm with a dressed green salad.