Scalloped Hasselback Potatoes

Preheat oven to 425 degrees F.

Make crosswise cuts every 1/8 to 1/4 inch along each potato, slicing almost to the bottom but not all the way through. Place the potatoes in an 8-inch-square baking dish and coat with cooking spray. Sprinkle with 1/4 teaspoon salt and 1/8 teaspoon pepper.

Bake the potatoes until the cuts begin to separate, 25 to 30 minutes. Remove from the oven; spray cooking spray into the opened cuts. Return to the oven and bake until the potatoes are tender, 30 to 40 minutes more.

When the potatoes are done, heat oil over medium-high heat in a small saucepan. Add onion; cook, stirring, until softened and beginning to brown, 2 to 3 minutes. Add 1/2 cup milk; cook, stirring occasionally, until steaming. Whisk the remaining 1/4 cup milk with flour in a small bowl until smooth; then whisk the mixture into the hot milk. Cook, stirring frequently, until bubbling and thickened, about 1 minute. Remove from the heat; add cheese and the remaining 1/8 teaspoon each salt and pepper. Stir until the cheese is melted.

Transfer the potatoes to a serving platter. Pour the cheese sauce over the potatoes. Sprinkle with paprika and thyme.