Step 1

Preheat the Oven - Set the oven rack to the middle position. Heat to 400ºF (200ºC).

Step 2

Prepare the Potatoes - Scrub, rinse, and dry the potatoes. Peel and slice into ⅛ inch-thick pieces using a mandoline.

Step 3

Make the Cream Sauce - Melt the butter in a large skillet over medium-low heat. Add the onions, and saute until fragrant, 2 minutes. Add the flour, whisk to combine, stir and cook for 2 minutes.Gradually whisk in the milk and cook until thickened over medium heat, 2 to 3 minutes. Turn off the heat and whisk in salt, pepper, and nutmeg. Add 1 cup cheddar cheese, and stir to combine.

Step 4

Assemble the Casserole - Grease the bottom and sides of an 8-inch square casserole dish. Layer half of the potatoes in overlapping rows. Sprinkle half of the ham over the potatoes. Spread half of the cheese sauce on top. Sprinkle ½ cup cheddar over the sauce.Layer the remaining potatoes, followed by ham and cheese sauce. Sprinkle with ½ cup cheddar cheese.

Step 5

Bake - Cover with foil and place on a baking sheet. Bake for 40 minutes. Remove the foil and continue baking until the potatoes are tender and the cheese is browned and bubbly, 20 to 25 minutes.

Step 6

To Serve - Transfer the dish to a wire rack and cool for 10 to 15 minutes before serving. Garnish with chives.