Pear and Red Onion Gratin

Fill a large bowl three-quarters full with water; add a handful of ice cubes. Cut onion into 16 wedges, place in a strainer and lower into the water. Let stand for 20 minutes. Preheat oven to 400 degrees F. Halve and core each pear; cut each half into 6 slices. Drain the onion wedges well and place them in a 9-by-13-inch glass baking dish along with the pear slices, 1 tablespoon oil, thyme, salt and a grinding of pepper; toss to combine. Cover with foil. Roast for 30 minutes, stirring twice. Meanwhile, combine breadcrumbs and cheese in a small bowl. Drizzle with the remaining 2 tablespoons oil; stir to combine. Remove the pan from the oven, sprinkle the crumb mixture evenly over the gratin, return to the oven and roast until the breadcrumbs are well browned, 20 to 30 minutes more. Let cool for 10 minutes before serving.