Vegan sausage rolls

Name: Vegan sausage rolls
Prep time: 20 min
Cook time: 50 min
Total time: 1 h 10 min
Cuisine: European, British
Ingredients: 250g chestnut mushrooms; 3 tbsp olive oil; 2 leeks finely chopped; 2 large garlic cloves crushed; 1 tbsp finely chopped sage leaves; 1 tbsp brown rice miso; 2 tsp Dijon mustard; 30g chestnuts very finely chopped; 70g fresh white breadcrumbs; 1 x 320g sheet ready-rolled puff pastry (not the all-butter version); plain flour for dusting; dairy-free milk (like soya milk), to glaze