Mushroom and Chestnut Wellington (Vegetarian)

• 500 g Puff pastry, all-butter preferred
• 500 g Mushrooms
• 1 large Yellow onion
• 40 g Butter
• 3 cloves Garlic
• 6 sprigs Fresh thyme
• 200 g Roasted chestnuts
• ½ tsp Black pepper, freshly ground
• 1 Egg yolk

1. Take the puff pastry out of the fridge so it is pliable but still cool. Finely chop the mushrooms, then finely dice the onion and crush the garlic. Strip the thyme leaves from the sprigs and roughly chop the chestnuts.
2. Melt the butter in a large frying pan over a medium heat, then add the onion and cook for 8 to 10 minutes until soft and lightly golden. Stir in the garlic and thyme and cook for 1 minute until fragrant. Add the mushrooms and cook for 12 to 15 minutes, stirring often, until the mixture is very dry and deeply savoury.
3. Stir the chestnuts through the mushroom mixture and season with the black pepper. Tip into a bowl and spread it out so it cools quickly. Chill until completely cold, otherwise the pastry will soften and split.
4. Heat the oven to 200°C (390°F) and place a baking tray inside to heat. On a lightly floured surface, roll the puff pastry into a rectangle about 3 to 4 mm thick. Pile the cold filling down the centre, then fold the pastry over to enclose it, pressing the seam and ends firmly to seal.
5. Whisk the egg yolk with 1 tsp water, then brush it all over the pastry. Carefully transfer the Wellington to the hot tray, seam-side down, and score the top lightly with a knife without cutting through. Bake for 30 to 35 minutes until deeply golden and crisp, then rest for 10 minutes before slicing.

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