Potato Gratin with Caramelized Onions & Prosciutto

Potato Gratin with Caramelized Onions & Prosciutto

Serves: 8 – 10

Potato Gratin with Caramelized Onions & Prosciutto 

Close up with yummy potatoes!

I must have the worse filing system for recipes. I pull them from magazines, newspapers, friends – anywhere and store them (not well) until I have the time and interest to give them a try. This is one such recipe. It was published in the LA Times under the banner of Best of 2009. I made it for Christmas Eve and served with Prime Rib – yes over indulgence!  But, it truly is amazing…so I remade it with a few modifications to share with you. There is no reason it should have taken that long to make it to the top of the heap of things to try…just needed the right occasion.

The caramelized onions can be prepared separately. In truth, the best time to caramelize onions is the day before. They do take some time to do it right. Often enough, you need to have them ready before you can start on the rest of the dish. But, you will be rewarded with a deep, rich, sweet flavor as the natural sugars in the onions caramelize. You can caramelize any type of onion – some just do so more quickly than others depending on their sugar content. Make some extra, as they are terrific on sandwiches, pizzas, over pastas, in soups on meat, fish and egg dishes and adorning appetizer platters. Store refrigerated for several days in an airtight container.

I use a mandolin to get the potatoes evenly and thinly sliced. This is one great tool, but easy to get a little of yourself in the dish if you are not careful. The metal ones from France can cost well over $100 but they can now be purchased for a third of the cost at department and kitchenware stores. It is a tool I use often and will share additional recipes in the near future featuring its use.

Caramelized onions:

• 5 pounds brown onions (about 6 large)
• ½ C olive oil
• 1 Tb salt

Gratin:

• 3 pounds waxy (low starch) potatoes, unpeeled
• (Such as Red potato, boiling potato or new potato, Peruvian purple potatoes and fingerlings – or, in a pinch, Yukon gold)
• 3½ C milk
• ½ C heavy cream
• 2 cloves garlic, crushed
• 1 bay leaf
• 2 tsp salt
• Butter
• 1 C caramelized onions
• 4 slices prosciutto, thinly sliced crosswise
• 3 ounces Gruyere, Comte or Emmentaler cheese, very thinly sliced or grated

As mentioned above, I recommend making the caramelized onions the day before. Cut off the stem and root ends of 5 pounds of onions, halve them lengthwise and peel away the dried brown skin. Cut the onions lengthwise into one-fourth-inch thick slices. Place in a heavy 7-quart pot. Pour ½ C olive oil and 1 Tb salt over onions, stir to combine. Set over medium heat, cover, and cook until the onions begin to wilt, stirring every 10-15 minutes to minimize sticking. As the onions soften, they will reduce in size quite dramatically.  After 20-30 minutes, they will be quite soft and will begin to stick to the bottom. Reduce the heat to low and continue cooking with the pot covered, stirring every 10 to 15 minutes to keep from sticking. After about 50 minutes, the onions will be silky and swimming in moisture. Remove the lid and increase the heat back to medium. 

Onions ready to caramelize

Mmmmmm.....getting close!

Cook, stirring frequently, until the moisture has mostly evaporated and the onions have begun to turn golden, about 30 minutes more. It will take another 20 minutes until the onions really begin to brown more deeply. Watch carefully to prevent sticking and burning. Continue cooking until onions have been reduced to a deep, reddish-brown marmalade. Set aside or refrigerate for future use.

Caramelized onions with red golden color

Heat the oven to 375 degree F and put a jellyroll pan in the bottom of the oven to catch any drips. Slice 3 pounds potatoes (unpeeled) as thinly as possible. A Japanese slicer, mandolin or V-blade is quite useful (see picture).

Slicing the potatoes with a Mandolin. Be careful!

Put the potatoes in a 3-quart saucepan and add 3½ C milk, ½ C heavy cream, 2 crushed garlic cloves, 1 bay leaf and 2 tsp salt. Cover and bring to a gentle simmer. When the liquid starts to bubble around the edges, remove the lid and cook until the potatoes are firm but tender, about 20 minutes in all. 

Ready to cook....

Rub the inside of a large gratin dish with a generous amount of butter. Using a slotted spoon, transfer about half the potatoes to the dish and arrange them in an even layer. Stir together the caramelized onions and 4 slices prosciutto and distribute evenly across the potatoes. It should be just enough to form a very thin layer.

Prosciutto for a little extra flavor

Pour the remaining potatoes and cooking liquid into the gratin dish, arranging the potatoes in an even layer. There should be enough liquid to almost cover the potatoes. Scatter 3 ounces grated Gruyere cheese over the top. Bake until the top is bubbly and evenly browned, about 1 hour.

The final product

This is a wonderful side dish for most any entrée. I served it with Prime Rib for a special meal but it also goes well with roasted chicken, turkey and any beef dish.

Enjoy!  We certainly did.

Larue