YIELD: one 9-inch galette
In a large bowl, combine the sugars, flour, cornstarch, spices, and salt. Add the pear and lemon juice and toss to combine.
Roll out the dough into a 12-inch round. Transfer to a parchment-lined sheet pan.
Arrange the pears in the center of the dough, leaving a 2-inch border around the perimeter. You can just pile them on or arrange in concentric circles. Pour any spare juices on top.
Fold edges over into the center, pleating the dough as you go. Brush the dough with egg wash and sprinkle with turbinado sugar. Refrigerate for 15 minutes.
Meanwhile, preheat the oven to 375 F.
Bake until the filling looks soft and jammy and the crust is golden brown, about 50 minutes. Cool slightly before slicing and serving.