For the filling:

• 30g (1oz) dried porcini mushrooms
• a large knob of butter
• 1 garlic clove, thinly sliced
• 4–5 thyme sprigs, leaves picked and chopped, plus extra leaves for sprinkling
• a small handful of sage, leaves picked and chopped
• 850g (1lb 14oz) minced fatty pork (belly is ideal)
• 2 teaspoons sea salt
• 2 teaspoons ground white peppercorns
• 100g (3½oz) fresh white breadcrumbs
• 1 egg, beaten with a splash of milk
• flaky sea salt, to finish

For the rough puff pastry:

• 150g (5½oz) unsalted butter, cubed and chilled
• 300g (10½oz) plain (all-purpose) flour, plus extra for dusting
• a good pinch of sea salt
• about 150ml (5fl oz) iced water

Place the dried mushrooms in a bowl and add enough warm water to just cover them. Stir them, then push them down into the liquid and allow them to soak for an hour or so.

While they’re soaking, you can make the pastry. In a bowl, combine the butter cubes with the flour and salt, then add just enough iced water to bring everything together into a dough full of big pieces of butter. On a well-floured surface, roll out the dough in one direction, away from you, to a rectangle about 1cm (½in) thick. Fold the two short ends into the middle so they overlap. Give the pastry a quarter-turn, and repeat the rolling, folding and turning process three more times (so you’ll have completed this process four times altogether). Wrap the pastry in baking paper and place it in the fridge to rest for 30 minutes (this stops the butter getting sticky). Remove the pastry from the fridge and repeat the rolling, folding and turning process a further four times. Wrap the pastry again and place it in the fridge to chill for 30 minutes.

Meanwhile, make the filling. Place a medium frying pan over a medium-high heat. Add the butter, and when it’s bubbling away, add the garlic and sizzle it for a moment or two.

Lift the mushrooms out of their soaking liquid, allow the excess water to drain from them, then scatter them into the pan. Season with a touch of salt and pepper and fry for 2–3 minutes, stirring every so often. Pour in the mushroom soaking liquid (except the last drop, which can be gritty) and give the pan a shake. Allow the liquid to simmer away until there is hardly any left. Now add the thyme and sage, turn them through the mushrooms, then remove from the heat and leave to cool.

Place the minced pork in a bowl and add the salt, white pepper and breadcrumbs. Roughly chop the cooled herby mushrooms, add these to the pork and mix well. Place the seasoned sausagemeat in the fridge while you roll out the pastry.

Roll out the pastry on a floured surface to a rectangle about 45 x 12cm (17¾ x 4½in) and 4mm (⅛in) thick. Lay the sausagemeat along one long side of the pastry, about 3cm (1¼in) in from the edge. Brush this pastry edge with a little egg wash and fold the other side of the pastry over the top of the filling to enclose it. Crimp the edges together well to seal.

Lightly brush the pastry with a little of the egg wash, then scatter over a few extra thyme leaves and a light sprinkling of flaky salt. Place the sausage roll in the fridge for 10 minutes or so to firm up. Meanwhile, heat the oven to 180°C/160°C fan/350°F/Gas 4.

Using a serrated knife, cut the sausage roll into 8–10 equal lengths and place them on a baking sheet lined with baking paper. Bake in the oven for 35–45 minutes, until golden brown. Transfer the sausage rolls to a wire rack to cool. Eat warm or leave to cool completely before serving. You can keep them in the fridge for a day or two.