Preheat the oven to gas 190°c / 390°f.
First, make the filling. In a saucepan, heat up a dash of olive oil and fry the onions until soft.
1 white onion
Add the garlic and mushrooms, then fry until the mushrooms have softened and most of the excess water has evaporated. Season generously with salt and pepper.
250 g chestnut mushrooms, 250 g portabello mushrooms, 4 cloves garlic
Drain in a sieve to make sure the mushroom mixture isn't too wet. Leave to cool.
Put the brazil nuts, breadcrumbs, thyme and mushroom mix in a food processor and roughly blitz. It should still be a bit chunky and not completely smooth.
100 g brazil nuts, 1 cup breadcrumbs, 1 tablespoon thyme
Pop the rolled pastry out on a floured work surface. Place the filling in a line in the centre of the pastry. Leave a couple of inches around the edges.
320 g puff pastry
Fold the edges over to seal it up, then brush the pastry edges with a little dairy free milk, and score the top lightly with a sharp knife – check the step-by-step photos for guidance (above).
Pop it on a baking tray and place in the oven and bake for around 30 minutes, or until the pastry is golden-brown.
20 ml plant milk
Once cooked, leave to stand for 5-10 minutes before slicing and serving.