http://www.ivillage.co.uk/food/partyfood/Chris tmas/articles/0,,164360_167390,00.html#mush
This link has a whole Christmas Dinner menu and recipes to make them - like this one:
Mushroom Wellington
Makes 2
This dish is time-consuming, but you can prepare it up to the baking stage and freeze it weeks in advance. Before serving, remove the wellington from the freezer and, after thawing, glaze the pastry with beaten egg and put it in a hot oven to bake for 45 minutes at 220C/425F/gas mark 7 until puffed and golden.
600g puff pastry
50ml sunflower oil
675g chopped onions
450g whole chestnut mushrooms
2 tbsp fresh tarragon
4 garlic cloves, crushed
4 tbsp soya sauce or tamari, or replace one with marsala or sherry
320g broken cashew pieces
320g ground almonds
175g fine freshly made breadcrumbs, white or wholemeal
1 egg, beaten for glazing
salt and pepper to taste
Roll out the pastry into two rectangles, 23x30.5cm each, cover and place in the fridge.
To make the filling, heat the oil in a large pan and fry the onion with half the crushed garlic for at least 20 minutes or until it turns a deep golden colour. This is crucial, as pale onions will give an insipid mix. Remove onions from the pan and set aside, then add the mushrooms to the same pan with the rest of the garlic and half the tarragon and cook on afairly high heat.
Halfway through cooking, add the soya sauce or tamari and the alcohol, if you are using it. Continue until the mushrooms are cooked through; there should be no white centre left when you cut one open. Season with salt and pepper. Set aside, reserving all the mushroom liquor (the intensely flavoured liquid given out by the mushrooms).
In a food processor or blen