Preheat the oven to 200c
Roll out a large piece of cling film, spread some of the mushroom mix to make a 7x4 inch rectangle thats 1 inch deep. Pop the tempeh at the edge of the mushroom layer and tightly roll over the tempeh. Twist the ends of the cling film so it holds tightly together, refrigerate for 15 mins to firm up.
Unravel the pastry with it still on its sheet. With the shortest edge nearest to you, pop on the tempeh.
Brush the pastry edges with a little milk. Fold the pastry over the tempeh and cut off excess pastry. Smooth over the seam to make sure it's sealed.
Pinch the sides together so it begins to look like a cracker, slice excess off till left with 1 inch, then push the sides in.
Lay the Wellington length ways on a large piece of clingfilm. Tightly roll and twist the ends.
At this stage the wellington can be left in the fridge overnight if you want to be super organised!
Whisk all pastry glaze ingredients together and brush over the Wellington.
Pop it on a tray seam side down, whack in the oven for 45-60 mins until the pastry is cooked and golden.
Serve with all the trimmings with lashings of our 15 min gravy!