A gluten-free hazelnut crust is teamed with a no-bake lemon curd filling and a toasted meringue topping in this bright, tangy dessert.
Preheat oven to 375 degrees. Pulse hazelnuts in a food processor until finely ground. Add confectioners' sugar, cornstarch, and salt; pulse to combine. Add egg white and butter and process until dough comes together. Transfer 2/3 cup dough to the bottom of a 9-inch fluted tart pan. With an offset spatula or the back of a spoon, spread and press in an even layer. Press remaining 1/3 cup dough firmly up sides of pan. Freeze until firm, about 15 minutes.
Blind-bake crust: Remove from freezer and prick all over with the tines of a fork. Bake until golden brown and dry, 20 to 25 minutes (if browning too quickly, tent edges with foil). Transfer to a wire rack; let cool completely. The tart shell can be baked up to two days ahead; store at room temperature.
Place 2 teaspoons cold water in a small bowl; sprinkle with gelatin. In a medium saucepan, whisk together granulated sugar, lemon zest and juice, yolks, and salt. Add butter, place pan over medium heat, and cook, whisking, until butter is melted. Continue to cook until mixture is thick enough to coat the back of a spoon and small bubbles form around edge of pan, 5 minutes more. Remove from heat and whisk in gelatin mixture. Strain through a fine sieve into a heatproof bowl, then pour into cooled crust. Refrigerate until filling has set, at least 2 hours.
Whisk together egg whites, granulated sugar, cream of tartar, and salt in the bowl of a stand mixer. Place over (but not in) a saucepan of simmering water. Cook, whisking frequently, until mixture is warm to the touch and no longer feels grainy when rubbed between two fingers. Transfer bowl to a stand mixer fitted with the whisk attachment; beat on high speed until stiff peaks form, about 5 minutes. Add vanilla and beat 1 minute more. Transfer meringue to a piping bag fitted with a large round tip (such as Ateco #808). Pipe large rounds around perimeter of tart. Brulee meringue with a kitchen torch, if desired. Serve.
You can swap out the meringue for lightly sweetened whipped cream.