1 teaspoon unsalted butter
2 tablespoons olive oil
6 ounces bacon, cut into 3/4 inch pieces
2 large yellow onions, peeled and thinly sliced
Freshly ground black pepper
6 ounces baby spinach
5 pounds white potatoes, washed and scrubbed and cut into 1/4-inch thick slices
8 ounces grated Gruyere, or Swiss cheese
4 cups heavy cream or half-and-half
Preheat the oven to 400 degrees F. Lightly grease a 2-quart baking dish with the butter and set aside.
Place the half and half in a large saucepan and bring to a simmer over medium-high heat. Add salt and pepper, and stir well.
Add the potato slices, adding more half and half if necessary to completely cover the potatoes. Lower the heat to medium-and simmer stirring so that mixture doesn’t burn until the potatoes are barely fork tender, about 10 to 12 minutes. Remove from the heat.
Take the sliced onions and sautee them with olive oil and butter until they are caramelized golden brown. Take the bacon and cook over low heat with olive oil and butter until warm. Sautee the spinach with olive oil until it is all wilted.
With a large spatula, transfer 1/3 of the potatoes with some of the cream to the prepared dish, forming an even layer on the bottom. Sprinkle 1/3 of the bacon, caramelized onions and spinach. Top with 1/3 of the cheese.
Continue layering the potatoes, onions, bacon, spinach and cheese, ending with cheese on top.
At the end, you should have about 1 1/2 to 2 cups of the half and half remaining
Place on a baking sheet and roast until golden brown and bubbly, about 30 minutes.