1/4 cup unsalted butter, at room temperature, plus 2 tablespoons cold butter, cut into pea-sized cubes
1/4 cup plus 3 tablespoons sugar, divided
1/2 cup almond flour
2 eggs, divided
2 teaspoons all-purpose flour
1/8 teaspoon vanilla extract
Garnish: chopped pistachios and hibiscus powder (optional)
Make the crust: In a food processor, pulse flour, sugar, and salt until combined. Add butter and pulse until mixture resembles sand with a few pea-size pieces. Add ice water, 1 tablespoon at time, until mixture comes together. Turn dough onto a work surface and divide in half. Wrap each half with plastic wrap, flatten, and refrigerate for at least 1 hour, preferably overnight (for a flakier crust).
Make the filling: Using a paring knife, slice tops and bottoms from citrus, then cut away the outer peel and pith. Slice citrus into 1/3⅓-inch rounds. Set aside on a sheet tray lined with parchment.
Using a stand mixer fitted with paddle attachment, cream .1/4 cup room-temperature butter and 1/4 cup sugar on medium speed for 2 minutes. Stop mixer, add almond flour, and beat on medium speed for 1 minute. Stop mixer again and scrape sides and bottom of bowl. With mixer on low speed, incorporate 1 egg. Stop mixer and add all-purpose flour, vanilla, and salt. Mix until combined well. Set aside.
Assemble the crostata: On a well-floured work surface, roll out one disk of dough into a circle 12 inches wide and about 1/8⅛-inch thick. Transfer dough to a sheet tray lined with parchment.
Spoon almond mixture onto center of dough and, using a spatula, spread mixture evenly across dough, leaving a 3-inch border. Arrange citrus over top, alternating sizes to create dimension, covering all almond filling.
Carefully fold the 3-inch border up and over the edge of the fruit, making loose pleats. Wrap crostata with plastic wrap and refrigerate for at least 1 hour.
Preheat oven to 350 degrees. Whisk remaining egg for an egg wash, then brush on edges of pleated dough. Sprinkle dough and citrus with remaining 3 tablespoons sugar. Drop remaining 2 tablespoons butter over to prevent fruit from drying while baking. Bake for 1 hour or until golden brown and bottom is evenly baked. Remove and let cool on a wire rack. After 10 minutes, lightly brush citrus with honey for a glossy finish. Serve warm with scoop of vanilla ice cream and crushed pistachios.