This is another recipe I have been working on for years. I started with the traditional one from an old 50's French/American cookbook and slowly evolved it over the years. I had forgotten about it until I was going through stuff to purge and I came across a few note pads that were stuffed in a kitchen box from when we sold our place in PA.
Over the years I have added and removed several different roots vegetables until I settled on this combination, of potatoes and onions.
3 to 4 lbs of heirloom potatoes - Sliced
1 lb of heirloom onions, I use whatever I can find, cut into 1/8 wedges or 1/6 wedges
1 leek, white parts, diced
2 shallots, minced
2 garlic cloves, minced
2 sprigs of thyme and rosemary - cut up.
2 tablespoons unsalted butter - plus more for pan
2 1/4 cups of half & half
1/2 cup of grated Gruyere
Fresh ground nutmeg - to taste
Salt and Pepper to taste
Preheat the oven to 400 degrees
Place shallots, garlic, and leeks in a bowl and toss to combine
Grease a large baking dish or 12+ inch cast-iron skillet with butter - sprinkle with fresh ground nutmeg.
Start layering the potatoes slices on the bottom of the pan or skillet, overlapping as you go, once one layer is done, season with salt and pepper, and sprinkle with the shallot mixture, repeat until done with potatoes.
The last layer is the onion wedges: I tried adding the onions as a layer in the middle but it just was hard to layer the potatoes on top, and slices of onions just made everything wet.
So on top so that the liquids are released during the baking is best.
Next dot the top with the 2 tablespoons of butter pour half and half on top. Place in the oven uncovered for 10 minutes, remove, sprinkle with the herb sprigs and return to oven and bake until potatoes are tender about 15 to 20 minutes, remove from oven once tender, reduce the oven to 300 degrees, cover the top of the potatoes/onions with the grated cheese and return to oven until cheese is golden. Remove, late stand for 5 to 10 minutes before serving.