Preheat oven to 350F. Mix all dry ingredients for the seitan roast, except for the puff pastry, together in a large bowl.

Make a well in the center of the dry ingredients and pour in the wet ingredients: broth or water, soy sauce, and oil, a little bit at a time, while mixing with a spoon. If it is too wet, add wheat gluten 1 tablespoon at a time. If it is too dry, add water 1 tablespoon at a time.

Knead for at least 3 minutes. Roll the seitan dough into a cylinder shape shape and roll in foil, twisting the ends. You can wrap it with a layer of parchment paper, followed by the foil layer, if you do not want the foil touching the seitan. It should be well fitting and not loose, but not too tight that it doesn't have a little bit of room to expand during cooking. Place on a baking sheet and bake for 1 hour and 15 mins.

Meanwhile, prepare your duxelles. Make sure your puff pastry is thawing according to package directions as well. Place garlic, herbs, and shallots in a food processor, or finely chop them. Then, add the mushrooms to finely chop them as well, or do it by hand. Make sure that it is not processed. You want it finely chopped, not puréed.

Sauté the mushroom duxelles in a pan over medium high heat for 5-10 minutes, until the water from the mushrooms evaporates. Set aside until the seitan is done.

Remove the seitan when done, and increase the oven heat to 400F. You can also store the seitan in the fridge a night in advance.

Assemble your wellington. Roll out your puff pastry dough thin enough to cover the wellington by a couple inches on each side. For me, this was about 10x14 in.

Spread a thin layer of duxelles, the same size as the wellington, in the center of your puff pastry. Cover with your cooked seitan roast. Cover the seitan roast on all sides with the duxelles mixture.

Trim off any excess dough, and fold over the top and bottom of the dough to cover the wellington. Cut the same number of diagonal slits on either side of the wellington, I cut about 7. Alternate covering the wellington with a strip of dough from either side, forming a braid down the middle. Alternatively, you could just fold the pastry over the seitan roast, and cut some slits in the top. You may need to wet your fingers to help seal the dough.

Mix the vegan egg wash together and brush it over the wellington before putting it at the oven at 400F for 30 mins.