Au Gratin Potatoes

Preheat oven to 350 degrees F. Coat a 9-by-13-inch baking pan with cooking spray.

Place potatoes in a large saucepan and cover with water. Bring to a boil, reduce heat to medium and cook, covered, until barely tender, 10 to 12 minutes. Drain, cool and slip off skins.

Coarsely shred the potatoes in a food processor or with the large-holed side of a box grater.

Place onion, garlic, flour, salt, dry mustard, cayenne and black pepper in a food processor; pulse until finely chopped. Add 1/2 cup milk and process until smooth. Scrape into a medium saucepan and add the remaining 2 1/2 cups milk. Bring to a simmer over medium heat, stirring constantly. Simmer, stirring, until thickened, about 5 minutes. Remove from heat and stir in 1 cup Cheddar until melted.

Combine the potatoes and the cheese sauce. Transfer to the prepared pan. Combine the remaining 1/3 cup cheese, breadcrumbs and oil in a small bowl and mix with your fingers. Sprinkle the crumb mixture evenly over the potato mixture.

Cover the pan with foil and bake for 40 minutes. Uncover and bake until golden brown and bubbling, about 20 minutes more. Let stand for 10 minutes before serving.