1
Preheat oven to 350°F. Butter a 3-quart casserole dish with 1 ½ tablespoons of the butter.
2
Arrange 1/3 of the potato slices in an even layer on the bottom of the prepared casserole dish. It’s fine if they overlap a little. Sprinkle with salt and pepper. Cover with ½ the onion slices and 3/4 cup of the Gruyere. Top with 1/3 of the bacon, 1 tablespoon or so of parsley, and 1 tablespoon of chives. Sprinkle ¼ cup of Parmesan over the top.
3
Repeat by adding another layer of 1/3 of the potato slices. Sprinkle again with salt and pepper, then cover with the remaining sliced onions, ¾ cup of the Gruyere, 1/3 of the remaining bacon, 1 tablespoon of parsley and 1 tablespoon of chives. Sprinkle with another ¼ cup of Parmesan.
4
Top the layers with the remaining potato slices. Pour over the half and half. Dot the potatoes with the remaining 1 ½ tablespoons of butter.
5
Cover the dish tightly with aluminum foil and place in the preheated oven. Bake for 1 hour. Remove from the oven and uncover. Sprinkle with the remaining Gruyere, Parmesan, and bacon. Leave uncovered and return to the oven for an additional 30-40 minutes. When done, the top should be browned, the potatoes should be tender, and the liquid should be mostly absorbed.
6
Sprinkle with parsley and chives, if desired, before serving
