Mushroom impossible wellington

Vegetarian Thanksgiving main-dish success! Making all the components took a bit of time on Wednesday, but actually getting it in the oven on Thursday was painless. 

I'm so out of practice at this whole blogging thing that I didn't take good notes as I was going. So, this will be some rather vague hints, which you can take in any direction you like. If it helps, this is what the different filling components looked like:

The different filling components, from outside to inside:

• 2 portabellos, thinly sliced. Sear until juices are cooked off.
• 3 onions, thinly sliced. Caramelize in olive oil; season with salt, pepper, and a generous amount of fresh herbs (rosemary, marjoram, sage); deglaze with apple cider vinegar. After cooking down, this made a bit less than 1 pint. Half went into the impossible filling, and the other half was its own filling layer.
• 1 lb crimini mushrooms (minced) + 1/2 lb oyster mushrooms (roughly torn). Cook in butter until juices are cooked off; season with salt, pepper, and truffle oil; deglaze with balsamic. After cooking down, this made a bit more than 1 pint.
• 1 pack (12 oz) impossible ground beef, with the following kneaded in by hand: half the caramelized onions, 6 cloves of garlic (minced), 1 T mustard, pumpkin seeds (roughly chopped, perhaps 1/4 c - 1/2 c?). Mold into a cylinder that's as long as you want the final wellington to be, and sear until browned on all sides (similar to making one huge kofta).

To assemble the fillings: Lay out a big piece of plastic wrap (I overlapped two pieces to get it wide enough). Space out the portabello slices to cover a rectangular area that's as wide as your impossible log, and a bit longer than the diameter of the log. Spread the remaining half of the caramelized onions over the portabellos, then spread the other mushrooms over the onions. Place the impossible log on the end of the rectangle, and use the plastic wrap to roll it up into a log.

Before and after rolling:

I did all that on Wednesday afternoon, and put the plastic-wrapped filling log in the fridge overnight.

For the crust, I used the rough puff from Bon Appetit. I made a full recipe (2 lb) on Wednesday, wrapped it in plastic, and put in the fridge overnight. On Thursday, I sliced off used half of it (1 lb) for the wellington. The other half is in the freezer for another adventure soon, maybe apple turnovers?

To assemble and bake: Preheat the oven to 425F. Roll out the crust to a rectangle ~2 inches larger in both dimensions than the filling rectangle was. Beat an egg with a splash of milk, and brush a bit on 3 edges of the rectangle. Unwrap the filling log from its plastic, and carefully transfer onto the un-egged edge of the crust (I did this by rolling it off from the plastic, since the outer layers were falling off a bit). Roll the log up in the crust, and tightly seal the 3 egged edges. Transfer to a parchment-lined baking sheet, brush with more egg wash, and gently score the surface in a diamond pattern with a long knife. Bake for 30 min at 425F, then turn down to 375F and bake for another 20 min until it's beginning to be golden brown even in the cuts. (I turned down the heat in order to get the pie baking too—if you don't have other oven needs, it might brown even better if you keep the temperature higher.)