Preparation

Make the crust

Preheat the oven to 350°F. In a food processor, combine the pistachios and confectioners’ sugar. Pulse until the pistachios are finely ground.

In a medium bowl, whisk together ground pistachios, 1 cup flour, and the salt. Using a wooden spoon, stir in the melted butter until the dough comes together. (It won’t be crumbly like pie dough—it will be soft and sticky.)

Transfer mixture to a 9-inch tart pan with a removable bottom. Using lightly floured hands, press the dough evenly into the bottom and up the sides of the pan. Freeze the crust for 20 minutes before baking. Bake until set, 15 to 20 minutes. Transfer to a wire rack to cool.

Make the filling

In a small microwave-safe bowl, sprinkle the gelatin over the hot water, and let stand 5 minutes. Microwave for 20 seconds. Stir with a fork until fully dissolved; set aside.

Meanwhile, place a medium saucepan filled with an inch or so of water over medium-low heat, and bring to a gentle simmer. In a large heatproof bowl, combine the sugar and eggs. Add the passion fruit puree and lemon juice, and whisk to combine. Place the bowl over the simmering water, and whisk until the filling thickens and reaches 165°F on an instant-read thermometer.

Strain filling through a fine-mesh sieve into another large bowl. Whisk in the butter until melted and mixture
is smooth. Stir in the dissolved gelatin. Set filling aside for 10 minutes to cool.

Pour the filling into the cooled tart crust, and chill until set, at least 4 hours or up to 24 hours. (If chilling for 24 hours, cover with plastic wrap so it touches the filling to prevent a skin from forming.) When ready to serve, make the meringue.

Make the meringue and topping

In the bowl of a stand mixer fitted with the whisk attachment, combine egg whites and salt. Beat on medium speed until frothy, about 2 minutes. Reduce speed to low, then gradually add the sugar. Turn to high and beat until meringue is smooth and glossy and stiff peaks form, 2 to 4 minutes. Whisk in the rose water, if using.

Dollop the meringue on top of filling. Use a kitchen torch to brown the meringue all over (or broil in the oven until just starting to brown around the edges). Sprinkle with chopped pistachios and dried rose petals. Serve immediately.