1
Defrost the puff pastry according to package directions. Preheat the oven to 375 degrees F.
2
Place the mushrooms, stem side up, and the diced butternut squash on a baking sheet. Drizzle with a tablespoon of olive oil and season with salt, pepper, and the leaves from 2 sprigs of thyme. Bake until vegetables are tender, about 15 minutes. Remove from the pan and blot dry with paper towels.
3
In the bowl of a food processor, pulse the button mushrooms, walnuts, 1 tablespoon fresh thyme leaves, and rosemary until finely chopped.
4
Heat a tablespoon of olive oil in a saute pan over medium-low. Saute the shallot until translucent. Add the garlic and saute another minute more. Add the duxelles (mushroom mixture) to the pan and cook down until softened and most of the liquid has evaporated.
5
Meanwhile, in another pan, saute the spinach with salt and pepper in a teaspoon of olive oil until wilted. Squeeze out as much moisture as possible with a paper towel.
6
Bring the oven up to 425 degrees F. To assemble the Wellington, open one puff pastry sheet on a sheet of parchment paper. Roll to approximately a 10x12 inch rectangle. Spread half of the mushroom mixture over one long side of the pastry dough, about the same width as the portobellos. Leave a 2-inch boarder to seal the dough. Top the duxelles with the spinach, butternut squash, and portobello mushrooms. Add the remaining duxelles over the top of the portobellos.
7
Use a pastry brush to brush the milk over the perimeter of dough. Stretch the empty half of the dough over the log of filling. Seal the dough at the long and short ends and tuck under. Brush the top of the Wellington dough with more milk and lightly score with a knife. Bake until very golden brown and crisp, about 25 minutes.
8
Serve right away with gravy or cranberry sauce or chutney.
