Put the mushrooms in a blender, blend it until finely chopped. Wash and chop the leeks and the chestnuts. Grate the parmesan and leave it aside for later.

Then in a heated pan add olive oil with the chopped leeks and fry till they get softened and golden. When the leeks are soft and brown, take them out of the pan.

In the same pan add the rest of the olive oil and mushrooms. Add the garlic, sage, rice and mustard to the already fried mushrooms, and fry it again for a couple of minutes. Then leave aside to cool off.

Preheat the oven to 392°F (200°C). In the mushrooms mixture add fried leeks, after that add chestnuts, cheddar and breadcrumbs, add salt and black pepper to taste and mix everything together.

On a floured surface place the pastry, then roll out to make it thinner. Add the mushroom mixture in the center of the pastry. Cover the mixture with the pastry creating a roll, close the two ends with a fork and cut it into 8 pieces.

Lay the rolls on a previously prepared baking sheet, spred the beaten egg on top of them. Bake the rolls for around 20 minutes until they get golden brown.

Finally, allow them to cool off before eating.