Potato Gratin With Caramelized Onion and Prosciutto (Or Bacon)

I great dish that isn't a real quicky, but is worth the time, a great company dish. The carmalized onions take several hours, so good to make when you'll be puttering around the kitchen anyway, so you are nearby to stir them. They are definitely worth the time, a very rich tasting sweet and savory addition to the potato dish. They are SO good, and can be made up to a week ahead (kept in the fridge Got this from a magazine, but tore the page out and now don't know who to give credit too... oops.

• Ready In: 4 hrs 45 mins
• Serves: 8-10

Ingredients

• 5  lbs onions, yellow (about 6 very large)
• 1⁄2 cup  vegetable oil (see note below, in directions)
• 1  tablespoon salt
• 3  lbs  wax potatoes, unpeeled (about 7)
• 3 1⁄2 cups milk
• 1⁄2 cup heavy cream
• 2 -3  garlic cloves
• 2  bay leaves
•  butter
• 4  slices prosciutto, thinly sliced (or 6 slices bacon, cooked and crumbled)
• 6  ounces gruyere or 6  ounces  emmenthaler cheese, grated
•  white pepper (optional)

Directions

1. First, the caramelized onions:.
2. IN EACH STEP, YOU WILL NEED TO STIR ABOUT EVERY 10-15 MINUTES, UNLESS OTHERWISE NOTED.
3. Cut off stem and root ends of onions, and peel away the dried skin. Slice into 1/4" slices adn gather in a large, heavy bottomed pot. A 7 qt pot works perfectly.
4. Pour the oil and salt over onions and toss to combine. (NOTE: Because I fried bacon to use for the dish, I used 2 T of the bacon fat, and then added veggie oil to make up the 1/2 Cup. Gave a great other layer of flavor to the onions) Set over medium heat and cover. Cook until onions begin to wilt, for 20-30 minutes. (Don't forget the stirring!)
5. Reduce heat to low and continue cooking, with pot still covered, for 45 minutes. (are you still stirring?).
6. Remove the lid, increase heat to medium and cook (stirring) 30 minutes, or until most of moisture has evaporated.
7. Reduce heat to low and continue cooking for about 2 hours, stirring every 20 minutes.
8. Continue cooking and stirring for about 1 more hour. You'll need to watch more carefully now, stirring about every 10 minutes. Cook until onions have been reduced to a deep reddish-brown marmalade, watching that they do not dry out. When done, removed from heat and set aside to cool.
9. -----------------------------.
10. Slice potatoes as thinly as possible (a V-slicer works great). Place potatoes in a 3 qt heavy bottomed pot or saucepan and add milk, cream, garlic, salt and bay leaves. Cover and bring ust to a gentle simmer, then remove lid and cook until potatoes are firm but tender, 15-20 minutes.
11. Heat oven to 375 and put a large cookie sheet on bottom rack to catch drips. Position another rack in center of oven.
12. Rub inside of large gratin dish with generous amount of butter. Using a slotted spon, transfer about half of the potatoes to the dish, in an even layer. Stir together caramelized onions and bacon/prosciutto adn distribute evenly on top of potatoes (should be enough for a very thin layer). Top with 1/4 of the cheese.
13. Put the remaning potatoes in the dish, smooth to an even layer and pour cooking liquid on top. I like to shake on a good dusting of white pepper, but this is optional. Scatter the remaining cheese over the top and bake until top is bubbly and evenly browned.
14. Let sit for about 10-15 minutes before serving.