Yukon gold potato gratin

Certain recipes, taught at the beginning of a culinary student's training by an experienced chef, never need to be adjusted, tampered with or even improved upon. Potato gratin is one of those recipes. I revisit it four to five times each year, usually on holidays like Easter, Christmas or Thanksgiving. But don't wait for a holiday to make this always-welcome, always-delicious side dish. Among the qualities that recommend it are that it can be made in ahead, and reheats it well, though in my experience, leftovers are rare.

Yukon gold potatoes are my preference for a gratin, but russets or baking potatoes work fine too. Combined with thinly sliced yellow onions, Gruyere or Parmesan cheese, and enough heavy cream to top off the gratin--but not so much that the potatoes are soaking in it--this is one of those dishes that is truly greater than the sum of its parts. When preparing a gratin in the spring, note that the young potatoes available in the market are a bit too soft and waxy to hold their shape during the long baking time.  However, other spring items like young onions and green garlic make excellent additions. 

A mandolin is essential for slicing the potatoes and onions for a gratin. (See techniques). Be patient and deliberate when layering the ingredients, and remember that the ingredients themselves don't have to be distributed perfectly evenly. If patience is not part of your cooking vocabulary, toss the sliced ingredients in a large bowl to combine before pressing them into the gratin pan. There isn't much a little layer of cheese on top won't cover!  

Potato gratin is best served as an accompaniment to a hearty meal of roasted poultry, vegetables and a green salad.

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Makes one 12 to 14 inch round or oval gratin dish, or 6 to 8 servings

Ingredients

2 tablespoons unsalted butter, melted

12 medium-size Yukon gold potatoes, unpeeled

1 large yellow onion, peeled 

3 tablespoons coarsely chopped fresh thyme

3 cups grated Gruyere or other cows milk cheese (If it has been aged between 9 and 12 months, moisture content will be low.  This is preferable.)

1 cup heavy whipping cream

Salt and freshly ground black pepper

Procedure

Preheat the oven to 350 degrees F. Use a pastry brush or paper towel to coat an ovenproof baking or gratin dish with the melted butter.  Set aside.

Using a mandolin, thinly slice the potatoes and onion. You will want to work quickly now, as the potatoes will start to oxidize and discolor slightly as they sit.  Assembling all of your ingredients in advance will allow you to be efficient.

Begin by spreading two layers of potatoes on the bottom of the pan.  Next, add a loose layer of onion rings,  1/3 of the chopped thyme, a generous layer of grated cheese (about 3/4 cup), and a good pinch of salt and freshly ground black pepper. Repeat with two layers of potatoes, followed by more onions, cheese and thyme. Be sure to season each layer with salt and pepper.  Continue until the potatoes are gone and finish with a layer of cheese.  Pour the cream over the top of the gratin.  

Cover the top of the gratin with a piece of parchment paper, then wrap the pan with aluminum foil. (The parchment paper on top prevents the potatoes and cheese from discoloring when they make contact with the foil.) Place the pan in the oven and bake for 30 minutes.  After 30 minutes, remove the foil and parchment paper, and return the gratin to the oven for another 30 minutes. If a fork or skewer can be inserted into the middle of the gratin with no resistance,  it is ready.

Note that some of the potatoes in the photograph to the right have crispy, dark edges. If you like a bit of crunch on the top layer, increase the oven heat to 400 degrees F during the last 10 minutes of baking for additional browning.

Once you remove it from the oven, the gratin will stay fairly warm for 30 to 40 minutes. If it will be sitting longer before you serve it, place the gratin in a low oven for 10 to 15 minutes to reheat.