Position a rack in the center of the oven and heat the oven to 400°F. Let the dough sit at room temperature until pliable, 10 to 15 minutes.
Roll the dough between 2 sheets of lightly floured parchment paper into a 14-inch round, loosening the parchment from the dough occasionally and adding a bit more flour if it sticks. Transfer on the parchment to a large rimmed baking sheet; remove and discard the top sheet of parchment.
In a small bowl, whisk the egg and cream.
In a large bowl, combine the plums, lemon juice, and vanilla. In a small bowl, whisk the flour, 6 Tbs. of the sugar, the ground ginger, cinnamon, and 1/8 tsp. salt. Add the candied ginger, and use your fingers to disperse it evenly. Add the dry ingredients to the plums, and gently toss to combine. (If your plums are very tart, add sugar to taste.)
Leaving a 2-inch border, spoon the plum mixture over the dough. Fold the edge of the dough up and over the filling. If the dough is sticking to the parchment, refrigerate it for 5 to 10 minutes, and then continue folding. Brush the folded dough with the egg wash, and sprinkle the remaining 1 Tbs. sugar all over the galette.
Bake, rotating the baking sheet once halfway through, until the crust is golden brown, 45 to 55 minutes. Let cool on a rack for 10 to 15 minutes. Serve warm or at room temperature with the ice cream, if using.
nutrition information (per serving):
350, Fat Calories
15, Saturated Fat
9, Polyunsaturated Fat
1.5, Monounsaturated Fat
Photo: Scott Phillips