I made this as a Christmas dinner alternative to the amazing free range goose we had from http://www.goodmansgeese.co.uk
It was truly knockout. Great hot and great cold the next day. I served with roasties, braised red cabbage, roasted brussel sprouts and fig and plum sauce. Really easy to make. I used Jus-rol shortcrust pastry (which out of interest is suitable for vegans)
https://www.bosh.tv/recipes/portobello-mushroom-wellington the website is also very cool as it shows a video for each step which I found really helpful.
I would eat this any time of the year, it was a smash success!!!