- 2 3/4 pounds assorted root vegetables such as Yukon gold potatoes, turnips, sweet potatoes or rutabagas, peeled
- 2 tablespoons butter , plus more for pan
- 2 tablespoons flour
- 1 cup whole milk , heated
- 1 cup grated loosely packed white cheddar cheese (about 4 ounces before grating), plus 2' 'tablespoons for garnish
- 1 teaspoon fresh thyme leaves , plus sprigs for garnish
- 3/4 teaspoon salt , plus more as needed
- 1/2 teaspoon freshly ground pepper , plus more as needed
- 1 cup coarse fresh or packaged breadcrumbs
- 2 tablespoons butter , melted
- 2 teaspoons fresh thyme leaves
To make béchamel sauce: In a medium skillet melt butter over medium-low heat. Sprinkle flour over butter and whisk until flour is cooked and well combined, about 2 minutes. Whisking, pour in the hot milk. Continue to whisk until sauce is well combined and thickened, 3 to 4 minutes. Whisk in cheddar, thyme, salt and pepper, until cheese melts. Remove sauce from heat.
Butter sides and bottom of a 6-inch spring form pan. Layer vegetables in concentric circles covering bottom of the pan. Every 2 to 3 layers, press firmly with fingers to even out layers. (Vegetable rounds do not have to be perfectly overlapping or spaced.) Spread 3 to 4 Tbsp. béchamel over vegetables, salt and pepper as desired. Continue layering and spreading sauce until vegetables are a few layers over rim of pan. Sprinkle remaining grated cheese over top. (Completed gratin may be covered with plastic wrap at this stage and refrigerated up to 4 hours. Remove plastic wrap before continuing.)
To cook: Cover with foil and place on a baking sheet (to catch spills) in oven. Cook until heated through and vegetables are tender, 30 to 45 minutes; remove foil for last 15 minutes.
While gratin is cooking combine breadcrumbs, melted butter and thyme in a medium bowl. Arrange breadcrumbs in an even layer on a baking sheet. Toast in oven until golden, about 5 minutes. Set aside to use as garnish on gratin sides.
To serve: Let sit at room temperature about 5 minutes. Run a knife around inside of gratin. Open pan, remove sides, and using a large spatula, transfer to a serving platter. Press breadcrumb mixture around sides of gratin. Arrange thyme sprigs. Cut into wedges to serve.
Adapted from Back to the Table by Art Smith