Christmas mushroom log

Ingredients

• 2 tablespoons olive oil
• 1 large onion, finely chopped
• 2 sticks celery, finely chopped
• 1 large leek, finely chopped
• 500 g (5 cups) mushrooms, button or cremini, roughly chopped
• 3 cloves garlic, crushed or finely chopped
• 50 g (½ cup) walnuts, roughly chopped
• 1 teaspoon fennel seeds
• ½ teaspoon salt
• ½ teaspoon pepper (to taste)
• 1 tablespoon maple syrup
• 1 tablespoon balsamic vinegar
• 1 tablespoon nutritional yeast (or 1 teaspoon yeast extract, e.g. Marmite)
• handful (½ cup) fresh parsley, finely chopped
• handful (½ cup) fresh thyme, finely chopped
• 85 g (¾ cup) breadcrumbs or stuffing mix
• 250 ml (½ cup) vegetable stock
• flour for dusting
• 1 pack (500 g) puff pastry
• 50 ml (1/3 cup) almond or other plant-based milk