Savory Mushroom Wellington

Steps

1. Chop the mushrooms: Working in batches, pulse the cremini and shiitake mushrooms in a food processor until very finely chopped (about the texture of coarse breadcrumbs). Alternatively, chop them by hand with a sharp knife — it takes a few extra minutes but works just as well.
2. Brown the vegetables: Heat 2 tablespoons of the olive oil in a large skillet or Dutch oven over medium-high heat. Add the onion and shallots and cook, stirring, until softened and translucent, about 5 minutes. Add the mushrooms and the remaining 1 tablespoon of olive oil. Cook, stirring occasionally at first and more often toward the end, until the mushrooms release their liquid and it fully evaporates, and the mixture is deeply browned and almost dry, 15 to 20 minutes.
3. Season and deglaze: Stir in the garlic, thyme, rosemary, salt, and pepper and cook until fragrant, about 1 minute. Pour in the sherry and tamari and cook, scraping up any browned bits from the bottom of the pan, until the liquid is absorbed, about 2 minutes. Remove from the heat.
4. Add the lentil-walnut layer: Fold in the cooked lentils, toasted walnuts, panko, and Dijon mustard until evenly combined. Taste and adjust the seasoning — the filling should be savory and well-salted, since the pastry will mellow it. Spread the filling onto a plate or baking sheet and let it cool completely (you can speed this up in the refrigerator).
5. Heat the oven and prep the pastry: Preheat the oven to 400°F with a rack in the center. Line a large baking sheet with parchment paper. On a lightly floured surface, gently overlap the two sheets of puff pastry by about 1 inch and roll them together into a rectangle roughly 16 by 13 inches.
6. Shape the Wellington: Arrange the cooled filling in a tight log down the center of the pastry, leaving a 2-inch border on all sides. Fold the short ends over the filling first, then bring the long sides up and over, pressing gently to seal the seam. Roll the whole thing over so the seam is on the bottom and transfer it to the prepared baking sheet.
7. Score and glaze: Brush the top and sides with the glaze (whisk the non-dairy milk with the maple syrup first). Use a sharp knife to score a shallow decorative pattern — diagonal slashes or a chevron — taking care not to cut all the way through. Sprinkle with flaky sea salt.
8. Bake: Bake until the pastry is deeply golden brown and puffed, 40 to 45 minutes. If the crust is browning too quickly, tent it loosely with foil for the final 10 minutes.
9. Rest and serve: Let the Wellington rest on the baking sheet for 15 minutes before slicing — this helps the filling set so it holds clean slices. Use a serrated knife and a gentle sawing motion to cut into 6 thick slices, and serve with vegetarian gravy or mushroom gravy on the side.