1 For the wellington filling:
2 Melt the butter in a large pan over a moderate heat
3 Add shallots and garlic and cook gently until softened
4 Add the thyme and stir
5 Add the chopped Mushrooms, cook until there is little moisture remaining and they are golden
6 Add tarragon leaves and stir
7 Season with salt and freshly ground pepper
8 Leave mixture to cool
9 Heat a little oil in a pan and cook the spinach until wilted. Squeeze out as much liquid as possible. Set aside.
10 When the mushroom mixture is cool, add the spinach and generously season
11 To make the wellington:
12 Roll the sheet of puff pastry out onto a sheet of baking paper, measuring 25cm x 30cm, lighted dusted with a little flour
13 Fill the mushroom mixture in a log shape at the bottom of your sheet, leaving 2cm at each side
14 Roll the Pastry around the mushroom mixture
15 Pinch the wellington closed to seal and trim any excess pastry
16 Use a fork to gently score the pastry and brush all sides with the whisked egg
17 Place in the fridge for 1 hour
18 Preheat the oven to 200C
19 For the mushroom gravy:
20 Melt butter in a pan over a medium heat
21 Fry the onions until they are softened
22 Add the garlic and cook for another minute
23 Add the mushrooms and cook for 8 minutes until golden and liquid has evaporated, remove and set aside
24 In the same pan, melt the butter, then add the flour
25 Stir to combine and cook for about 2 minutes, stirring continuously
26 Add broth and salt and pepper and simmer on low until gravy has thickened
27 Add the closed cup mushrooms
28 To cook the wellington:
29 Place the Wellington, along with the baking paper underneath, onto a large baking tray
30 Bake for 25 minutes before leaving to rest for 10 minutes
31 Serve with mushroom gravy