In a medium-sized bowl, use a fork to whisk the flours, sugar, and sea salt together. Grate in the butter, using fingertips to massage butter into the flour mixture. When mixture is well combined and crumbly, drizzle in just enough water for it to hold together. (If you're new to homemade dough, add enough water to handle the dough easily – it will be fine.)

Mound dough into a disc, wrap tightly with plastic, and chill for an hour or longer.

Preheat oven to 450 degrees F. Line a rimmed baking sheet with parchment.

To prepare the filling, fold the pitted cherries, sugar, tapioca, lemon zest, sea salt, and cinnamon together. Set aside while you roll out the dough.

Take the cut parchment from the prepared baking sheet and dust very lightly with flour. On the parchment, roll out the dough into a rough 14-inch circle. Place parchment with dough round on the baking sheet.

Working very quickly, mound the filling in the center of the dough, doing your best to leave excess juices behind. (Paper towels can be used to sop up any running juices, if needed.) Fold the dough up in 4-inch sections and lightly press together. Brush with egg white, sprinkle with the remaining 2 tablespoons sugar, and slide into the oven. Immediately turn heat down to 425 degrees F and bake for 10 minutes. Rotate galette, turn heat to 375 degrees F and bake until galette is a deep golden brown and juices are bubbling, 20 - 25 minutes longer.

Cool for two hours before serving. Scoops of vanilla ice cream are optional.