• Butter, for the baking dish

For the Filling

• 2 tablespoons (30ml) olive oil
• 1 teaspoon truffled olive oil (optional)
• 3 to 4 large (115g) shallots, thinly sliced
• 2 cloves garlic, minced
• 2 ounces bacon or pancetta (about 2 strips), chopped
• 1 cup (70g) finely chopped brown mushrooms
• 3 pounds (1.4kg) butternut squash, peeled and cut into ¾-inch (2-cm) pieces
• 2 tablespoons chopped fresh flat-leaf parsley
• 1 sage leaf, finely chopped
• ½ cup (120ml) chicken stock
• Salt and freshly cracked black pepper

For the Crumble Topping

• ¾ cup (95g) all-purpose flour
• ¼ cup (30g) finely chopped walnuts
• 1 tablespoon brown sugar
• 1 tablespoon chopped fresh thyme
• 1 teaspoon salt
• Freshly cracked black pepper
• ½ cup (1 stick / 113g) cold unsalted butter, cut into ¼-inch (6-mm) pieces

Directions

1. Preheat the oven to 375°F (190°C). Generously butter a 2-quart (2-L) baking dish.
2. Make the filling: In a large pan, heat the olive oil and truffled olive oil, if using, over medium–high heat. Add the shallots, garlic, and bacon or pancetta, and sauté until the shallots are soft. Add the mushrooms and squash and sauté until the squash starts to soften and brown, about 15 minutes.
3. Add the parsley, sage, stock, and salt and pepper to taste; mix well. Pour the squash mixture into the prepared baking dish. Cover with foil and bake until just tender, about 30 minutes.
4. Make the crumble topping: Place the flour, walnuts, brown sugar, thyme, salt, and pepper to taste in a medium bowl. Add the butter and pinch with your fingers until the mixture is the consistency of coarse meal; there will still be some pea-size lumps of butter. Set the topping aside in the freezer until ready to use.
5. Remove the dish from the oven and uncover. Scatter the crumble topping over the squash and return the dish to the oven. Bake for 45 minutes more, or until the topping is golden brown. Serve warm or at room temperature.