Peel the onion, slice into halves and chop finely. Peel and mince the garlic.
Wipe the mushrooms and chop finely.
Heat the oil and the butter in a large frying pan or wok – sauté the onion and the garlic for a few minutes on a low heat. Add the mushrooms and cook for another couple of minutes.
Put all the contents from the pan into a large bowl.
Finely chop the pecans and add to the mix.
Add the ricotta, seeds and breadcrumbs, then season with some salt and black pepper.
Finely dice the beetroot and add to the bowl, mixing well.
Join 2 sheets of defrosted pastry together. Put the mushroom mixture in the centre – in a log shape – allowing enough space to wrap the pastry around the filling.
Use 1 sheet of pastry if needed, to join to the existing pastry, if you need more room to roll the wellington.
Whisk the egg with the milk. With a pastry brush, seal the edges of the pastry with the egg wash and fold over the pastry to make an oblong, brick shape.
Put onto a greased baking tray, with the pastry join underneath.
With remaining pastry sheet, cut into holly shapes. Use the egg wash to stick them on the top, then glaze these with the wash.
Make a few slits in the pastry to allow the steam to escape.
Bake in the oven for 40 minutes until golden brown.
