Step 1

Heat two tablespoons of the oil in a large non-stick frying pan and cook the sweet potato over a medium heat for five minutes, or until beginning to soften and brown, stirring regularly.

Step 2

Add the onion and leek and fry for 10 minutes more, or until softened. Stir in the garlic, spinach, cranberries, pecans, chestnuts and orange zest. Season well with salt and pepper and cook for five minutes more, stirring regularly until the filling mixture is well softened. Spread onto a large tray and leave to cool.

Step 3

Heat one tablespoon more oil in the pan. Add three of the mushrooms (stalks removed) to the pan, smooth-side down. Cook for two minutes, then turn and cook for further two minutes on the other side. Drain, stalk-side down, on kitchen paper.

Step 4

Roughly chop the remaining mushrooms and add to the same frying pan with the rest of the oil and fry for 2-3 minutes, or until lightly browned. Stir into the filling mixture, adjust the seasoning with salt and freshly ground black pepper to taste, and leave to cool.

Step 5

Preheat the oven to 200C/180C Fan/Gas Line a large baking tray with baking paper. Unroll the puff pastry on its lining paper onto a thin board or tray. Spoon half of the sweet potato mixture down the centre of the pastry, from one short end to the other, leaving a 2cm/¾in border at each end.

Step 6

Arrange the whole mushrooms, stalk-side up, in a row on top of the sweet potato mixture. Spoon the remaining filling mixture over and around the mushrooms, pressing gently with clean hands until completely covered.

Step 7

Brush the pastry around the filling lightly with soya milk. Bring the two short sides of the pastry up and fold over the filling. Do the same with the long sides to create a long, oblong parcel. Patch any tears with pastry so that there are no holes. If your pastry is smaller than 375g/13oz, you may not have room for all the filling, so don’t worry about using it all.

Step 8

Place the lined baking tray on top of the Wellington and carefully flip the parcel and board over so that the pastry joins are underneath. Remove the top board and lightly score the pastry with the tip of a knife. Brush with more soy milk and sprinkle with poppy seeds, if using.

Step 9

Bake the Wellington for about 45 minutes (longer if it has been chilled), or until the pastry is golden-brown and crisp, and the filling is hot throughout. Serve with vegetable gravy.