Ingredients
Equipment
Method
Make the filling
- Preheat the oven to 425°F.
- Line a rimmed baking sheet with parchment paper.
- Toss the squash with 1 tablespoon of the olive oil, 1/2 teaspoon of the salt, and 1/4 teaspoon of the pepper.
- Spread the squash in a single layer and roast for 25–30 minutes, until tender and browned at the edges.
- While the squash roasts, heat the remaining 1 tablespoon olive oil in a 12-inch skillet over medium-high heat.
- Add the mushrooms and cook for 10–14 minutes, stirring often, until their liquid has evaporated and they are browned.
- Add the shallots, remaining salt, and remaining pepper and cook for 3 minutes.
- Stir in the garlic and thyme and cook for 1 minute.
- Transfer the squash to a plate.
- Reduce the oven temperature to 400°F.
- Remove the skillet from the heat and stir in the panko.
- Gently fold in the squash.
- Spread the filling on a plate and refrigerate until completely cool, about 30 minutes.
Assemble and bake
- Let the baking sheet cool, then line it with fresh parchment.
- On another large piece of parchment, arrange the pastry sheets side by side, overlapping them by 1 inch.
- Press the seam together and roll the pastry into a 12x16-inch rectangle.
- Shape the cooled filling into an 11-inch-long, compact log down the center of the pastry.
- Beat the egg with the water.
- Brush one long edge of pastry with egg wash.
- Fold the opposite edge over the filling, overlap with the brushed edge, and press to seal.
- Fold the ends under and place the Wellington seam-side down on the lined baking sheet.
- Brush the top and sides with the remaining egg wash.
- Cut a few shallow diagonal slashes in the pastry.
- Bake at 400°F for 35–45 minutes, until the pastry is deeply golden and crisp.
- Rest the Wellington for 10 minutes before slicing.
Notes
For cleaner slices, let the filling cool completely before wrapping. Refrigerate leftovers in an airtight container for up to 3 days; freezing is not recommended after baking because the pastry can soften. For a gluten-free variation, use gluten-free puff pastry and breadcrumbs.
