Radish & Potato Gratin

Arrange oven rack 8 inches from heat source; preheat broiler to high. Coat a 10-inch cast-iron skillet with cooking spray.

Place potato and radish slices in a large microwave-safe bowl and add 1/4 cup water. Cover with vented plastic wrap and microwave on High until just tender, about 5 minutes. Drain. Arrange the slices in the prepared skillet.

Whisk evaporated milk, Gruyère, flour, salt and pepper in a medium bowl. Pour the mixture over the vegetables. Bring to a boil over medium-high heat. Reduce heat and simmer until the vegetables are fully tender and the sauce is thickened, 10 to 12 minutes.

Mix panko and oil in a small bowl. Sprinkle evenly over the vegetables. Place the skillet under the broiler and broil until the sauce is bubbly and the topping is golden brown, 1 to 2 minutes. Let sit for 10 minutes before slicing. Served topped with chives.