1/2 cup (1 stick) cold unsalted butter, cut into small pieces
2 to 4 tablespoons ice water
For the plum filling:
1 tablespoon all-purpose flour, plus more for dusting
2 tablespoon whole raw almonds, toasted
1/4 cup granulated sugar, divided use
3-4 plums, halved, pitted, and sliced 1/4 inch thick (keep sliced halves together)
1 tablespoon heavy cream, for brushing
Instructions
Pulse flour, salt, and sugar in a food processor (or whisk together by hand in a bowl). Add butter and pulse (or quickly cut in with a pastry blender or your fingertips) until mixture resembles coarse meal, with some larger pieces remaining. Drizzle 2 tablespoons water over mixture. Pulse (or mix with a fork) until mixture just begins to hold together. If dough is too dry, add 2 tablespoons more water, 1 tablespoon at a time, and pulse (or mix with a fork).
Gather dough into a ball, wrap loosely in plastic wrap, and press each into a disk using a rolling pin. Refrigerate until firm, well wrapped in plastic, 1 hour or up to 1 day. (Dough can be frozen up to three months; thaw in refrigerator before using.)
Preheat oven to 350 degrees F. On a lightly floured piece of parchment paper, roll out dough into an approixmate 8-inch oval, 1/4 inch thick. Transfer dough (on parchment) to a baking sheet.
Pulse almonds, 3 tablespoons sugar, and the flour in a food processor until ground to a coarse meal. Sprinkle almond mixture over dough. With a spatula, transfer plum slices to dough, spacing close together and leaving a 2-inch border; press lightly to fan out. Fold edge of dough over fruit. Refrigerate 30 minutes.
Brush dough with cream; sprinkle galette evenly with remaining 1 tablespoon of sugar. Bake until crust is deep godlen, and plums are juicy and bubbling, about 40 minutes. Transfer to a wire rack, and let cool completely.