Artichoke-Potato Gratin

Preheat oven to 325 degrees F. Coat a 9-by-13-inch baking dish with cooking spray.

Heat oil in a medium skillet over medium-high heat. Add leek and cook, stirring, until wilted and browned in a few spots, 2 to 3 minutes. Transfer to a plate to cool.

Combine cream, 3/4 cup milk and salt in a medium saucepan and heat over medium heat until steaming. Whisk the remaining 1/4 cup milk and cornstarch in a small bowl until smooth. Whisk the cornstarch mixture into the cream mixture and cook, whisking, until slightly thickened, 2 to 3 minutes. Remove from heat. Add 1 3/4 cups Parmesan and stir until melted.

Coarsely chop artichokes and pat dry. Arrange one-fourth of the potatoes in the prepared baking dish. Season with 1/4 teaspoon pepper and top with half the artichokes. Layer on another fourth of the potatoes, half of the leek and half the capers. Layer on another fourth of the potatoes and season with 1/4 teaspoon pepper. Top with the remaining leek, artichokes, capers and potatoes and season with the remaining 1/4 teaspoon pepper. Pour the cheese sauce over the top and press with the back of a wooden spoon. Sprinkle with the remaining 1/4 cup Parmesan.

Bake until the top is golden brown and the potatoes are tender, about 1 hour 25 minutes. Let stand at room temperature for 10 minutes before serving.