FOR THE CRUST
¾ teaspoon fennel seeds (optional)
8 ounces shortbread cookies (such as Lorna Doone; about 30 cookies)
4 tablespoons unsalted butter, melted
FOR THE FILLING
1½ cups peeled roasted chestnuts (sold in bags or jars)
½ cup sugar
2½ cups heavy cream
1 vanilla bean, split lengthwise, seeds scraped out
4 tablespoons unsalted butter
2 large eggs
FOR THE MERINGUE
½ cup sugar
¼ teaspoon cream of tartar
Pinch of salt
4 large egg whites
1.Make the crust: Preheat the oven to 350˚. Toast the fennel seeds in a small dry skillet over medium heat until fragrant, about 2 minutes. Pulse the cookies in a food processor until finely ground. Add the fennel seeds and melted butter; pulse until moistened. Press the mixture evenly into the bottom and up the side of a 9-inch pie plate. Bake until lightly browned and set, about 8 minutes; let cool completely.
2. Make the filling: Combine the chestnuts, sugar, 1 cup heavy cream and the vanilla seeds and pod in a medium saucepan. Bring to a boil, then reduce the heat to low and simmer, stirring occasionally, until the cream is very thick and the chestnuts are softened, 25 to 30 minutes.
3. Meanwhile, melt the butter in a small saucepan over medium heat; cook until it smells nutty and is golden brown, about 4 minutes. Discard the vanilla pod from the chestnut mixture; transfer the mixture to a food processor, add the browned butter and process until smooth. With the machine running, slowly add the remaining 1½ cups heavy cream and the eggs; process until combined. Let stand until thickened and cooled, about 1 hour.
4. Carefully pour the filling into the crust (it will be full). Bake at 350˚ until the filling is set, about 45 minutes. Transfer to a rack and let cool completely.
5. Make the meringue: Bring a few inches of water to a boil in a large saucepan. Whisk the sugar, cream of tartar, salt and egg whites in the bowl of a stand mixer. Set the bowl over the boiling water (don’t let the bowl touch the water); continue whisking until the mixture is hot (135˚) and the sugar dissolves, 2 to 3 minutes.
6. Transfer the bowl to the stand mixer; beat with the whisk attachment on medium-high speed until soft peaks form, about 2 minutes. Increase the speed to high and beat until stiff, thick and glossy, 2 to 3 more minutes. Spread the meringue on top of the pie. Toast with a kitchen torch.