Root Vegetable Gratin

Preheat oven to 400 degrees F. Coat a 9-by-13-inch baking dish with cooking spray.

If using parsnips, quarter lengthwise and remove the woody core before cutting into 1/8-inch thick slices. Cook vegetables in a large pot of boiling water until barely tender, about 5 minutes. Drain.

Heat 2 tablespoons oil in a medium saucepan over medium heat. Add shallots and cook, stirring occasionally, until light brown, 3 to 4 minutes. Add 1 cup milk and bring to a simmer. Combine flour and the remaining 1/3 cup milk in a small bowl to make a smooth paste; stir into the hot milk and cook, whisking constantly, until the sauce bubbles and thickens, 1 to 2 minutes. Remove from the heat. Stir in 3/4 cup cheese, thyme, salt and pepper.

Combine breadcrumbs, the remaining 3/4 cup cheese and 1 tablespoon oil in a bowl.

Layer the vegetable slices in the prepared baking dish. Pour the cheese sauce over the top and top with the breadcrumb mixture.

Bake the gratin until it is bubbling and the top is golden, 30 to 40 minutes. Let cool for 10 minutes before serving.