Rustic Plum Crostata With Lemon Thyme

In a food processor fitted with a steel blade, pulse together the flours, 1 tablespoon sugar and 1/2 teaspoon salt until blended.
In a measuring cup, lightly beat the egg, and add just enough cream to get to 1/3 cup.
Lightly whisk the egg and cream together.
Add the butter to the flour mixture and pulse to break up the butter.
Do not over-process; you need lima-bean-size chunks of butter.
Drizzle the egg mixture over the dough and pulse until it just starts to come together but is still mostly large crumbs.
Put the dough on the counter and knead to make one uniform piece.
Flatten into a disk, wrap in plastic and chill for 2 hours or up to 3 days.
Heat the oven to 375 degrees.
Roll the dough out to a 12-inch round (it can be ragged).
Transfer to a rimmed baking sheet and chill while preparing the filling.
Toss together the plums, all but a tablespoon of the remaining sugar, a pinch of salt and the cornstarch.
Pile fruit on the dough circle, leaving a 1 1/2-inch border.
Gently fold the pastry over the fruit, pleating to hold it in (sloppy is fine).
Brush pastry with cream.
Sprinkle remaining sugar on top, with the thyme.
Bake for 30 to 40 minutes, until the crust is golden and the fruit is tender.
Cool for 5 minutes, then transfer to a wire rack.
Remove the thyme branches (some leaves will cling; you want this).
Serve warm or at room temperature.