Dough

1 cup plus 2 tablespoons all-purpose flour, plus extra for shaping

1 cup plus 2 tablespoons pastry flour

½ cup plus 1 tablespoon corn flour or fine cornmeal

2 teaspoons granulated sugar

1 teaspoon kosher salt

2 sticks (16 tablespoons) cold unsalted butter, cut into ½-inch cubes

3 to 4 tablespoons ice water

Galette

5 cups (2½ pints) fresh blueberries

½ cup granulated sugar, divided

1¼ teaspoons cornstarch (if using plums use 1 extra teaspoon)

Zest of 2 lemons, plus 1 tablespoon fresh lemon juice, divided

1 large egg, lightly beaten

1 teaspoon fresh thyme leaves

1 cup mascarpone