Ginger and Vanilla Bean Rhubarb Galette

SERVES 6

FOR THE DOUGH

1 ½cups (190 g) all-purpose flour, plus more for work surface

1 tablespoon sugar

½ teaspoon kosher salt

1 stick (½cup/115g) very cold unsalted butter, cut into small pieces

⅓ cup plus 1 tablespoon (90 ml) very cold buttermilk, well shaken

1 large egg, for brushing the crust

Raw sugar, for sprinkling

FOR THE FILLING

1 pound (455 g) rhubarb, trimmed and cut into 3-inch (7.5-cm) pieces, halved lengthwise if large

¾ cup (150 g) sugar

2 tablespoons all-purpose flour

1 tablespoon fresh lemon juice

1 tablespoon minced fresh ginger

1 vanilla bean, cut lengthwise, seeds scraped and pod reserved for another use (or 3 teaspoons vanilla extract)

Vanilla ice cream, for serving

Make the dough:

In a food processor ftted with a metal blade, pulse together the four, sugar, and salt until combined. Scatter the cubes of butter over the dry ingredients and pulse a few times until the butter is broken up and the mixture resembles a coarse meal. Slowly pour in the buttermilk, pulsing to combine, just until the dough begins to hold together. Transfer the dough to a clean work surface and shape into a square disc. Wrap the dough in plastic and refrigerate for a minimum of 1 hour or up to overnight. The dough can be made up to 2 days in advance and refrigerated. Preheat the oven to 400ºF. Line a baking sheet with parchment. On a lightly foured work surface, roll the dough into an approximately 10- by 14-inch (25- by 35-cm) rectangle. Carefully transfer to the baking sheet and refrigerate briefly while you prepare the filling.

Make the filling:

In a large bowl, toss all of the ingredients together until well combined. Use your fngers to break up any clumps of vanilla seeds; they should be distributed evenly throughout the flling. Pour the flling onto the center of the dough, leaving a 2- to 3-inch border along the edges. Fold the edges up over the filling and press gently to seal. Make an egg wash by whisking the egg with 1 tablespoon water. Brush the dough with the egg wash and sprinkle with raw sugar. Bake until the crust is golden and the fruit is bubbling, 30 to 35 minutes. Transfer to a wire rack and cool slightly before serving with a scoop of vanilla ice cream.