Make the crust: Pulse the flour, sugar and salt in a food processor. Add half of the butter and pulse until the mixture looks like coarse meal. Add the remaining butter and pulse into pea-size pieces. Add 1/4 cup ice water and pulse until the dough clumps together but has not yet formed a ball. Turn out the dough onto a piece of plastic wrap; press into a disk and wrap. Refrigerate until firm, at least 1 hour or overnight.
Meanwhile, make the filling: Pulse 1/2 cup almonds, 1/4 cup sugar, the egg yolk, butter, vanilla and lemon zest in a food processor to make a paste.
Preheat the oven to 400 degrees F and line a baking sheet with parchment paper. Roll out the dough into a 12-inch round on a lightly floured surface. Transfer the dough to the prepared baking sheet. Spread the almond filling over the dough, leaving a 2 1/2-inch border; top with the grapes. Fold the edge of the dough over the fruit by about 2 inches, pleating as needed. Refrigerate until firm, 30 minutes.
Lightly beat the egg yolk with 1 tablespoon water. Brush the dough with the egg wash. Scatter the remaining 2 tablespoons almonds all over the galette, then sprinkle with the remaining 2 tablespoons sugar. Bake until the crust is golden brown and the grapes are softened, about 40 minutes. Let cool on the baking sheet.
Photograph by Con Poulos
Courtesy of Food Network Magazine