Holidays, Potatoes, Random Thoughts, Science, Vegetables

Gratinizing.

This summer was the warmest weather on record for DC, and New York, with 52 days over 90F in June, July, and August, and no relief at night. Those sweaty days are a distant memory now – the entire east coast, from the Carolinas to New England, is either digging out from under a couple of feet of snow or being slapped by 35 mph winds. A thick, even coating of salt spray coats my car, and the gales in Baltimore are so strong that even the interior doors are rattling.

Seasonal eating! That’s why we do it. During the hottest days in July and August, we ate nothing heavier than chilled zucchini soup and completely raw salads of peaches and corn. Melons went straight from the refrigerator to the blender with a squeeze of lime; tomatoes, sliced thickly and spread with cooling mayonnaise, dripped juice into a thick slice of sourdough. Today, though, the shiny and identically pale pink tomatoes in the supermarket are about as inviting as the rock-hard, sour peaches from the southern hemisphere. When the temperatures head south of freezing, it’s time to turn on the oven and start thinking about braised meats, turnips, cabbages, potatoes.

It is no secret that potatoes are my favorite food and I look forward to autumn every year so I can cook all the potato dishes I want and more. Tonight, on the way home from the office, my husband and I stopped at My Organic Market to pick up some vegetables. As always, I was drawn to the potatoes. This time, though, I spotted something unusual: the heart-shaped potato.

Our potato god.

I put the heart-shaped potato in the basket. “This is very exciting. I’m going to buy it,” I informed my husband.

“Excellent,” he said. “Are we going to worship it?”

I thought about that for a moment. “Yes. It will be our potato god.”

The heart-shaped potato was of particular interest to me not merely because of its deistic qualities but because the USDA maintains fairly particular standards for grading produce for sale to the public. Potatoes, for example, generally must be classified as No. 1 to be sold as whole, unprocessed raw produce at retail. Among other things, U.S. No. 1 potatoes must be “fairly well shaped,” which means such a potato has “has the normal shape for the variety,” and “is not materially pointed, dumbbell-shaped or otherwise materially deformed.” A “seriously misshapen” potato – one which does not meet even U.S. No. 2 standards – is “seriously pointed, dumbbell-shaped or otherwise badly deformed.”

So what of the heart-shaped potato? By no means is this the “normal shape for the variety,” Russet Burbank to be exact. At the same time, however, I have a hard time imagining a potato grader giving the heave-ho to a heart-shaped potato. Who would be so cold? I picked up two heart-shaped potatoes tonight, as a matter of fact (the other one bore a closer resemblance to the state of Michigan in 3-D and was perhaps a more marginal candidate for retention). And just to hedge my bets, I put two Yukon Golds in the basket as well.

Yukon Golds (medium starch, non-deistic)

What were my plans for these potatoes? Just before Christmas, the New York Times T magazine interviewed Aki Kamozawa and Alex Talbot of Ideas in Food. The culinary innovators stated in closing that they were “bringing back the potato gratin.” I actually started from my seat (and bumped into my desk, since I was reading the piece in the office), since I too am bringing back the potato gratin. Of all the great, classic potato dishes, potato gratin has the potential to involve the most work for the lowest payoff. The best gratins feature thinly sliced potatoes, layered atop each other and pressed into a soft cake of multiple layers. More often, though, the resulting dish is a series of slippery, too-distinct layers, separated by a mass of curdled protein and grease, not a thick, firm, and creamy potato cake. You go through the hassle of slicing all those potatoes, layering them in a gratin dish in precise overlapping shingles, seasoning each layer and pouring cream over all, and in the end the whole thing isn’t all that great.

I’m not sure why – maybe it’s something in the water of the mid-Atlantic – but this year, I decided to change my gratinizing technique. The time just seemed right. I knew from making various pasta gratins, for example, that the best way to prevent melted cheese from separating and clumping is to make a mornay sauce, which is basically a béchamel with grated cheese whisked in. In the classic mornay sauce, the starch from flour keeps the cheese proteins from clumping together as they melt. I wasn’t planning to bake the potatoes in mornay sauce – you don’t need or want cheese in a classic potato gratin – but the lesson is to protect the dairy proteins with starch. Sliced potatoes release quite a bit of starch, and it seemed to me that potato starches could serve the same purpose as the flour in a mornay sauce – to coat the dairy protein and prevent it from clumping together. How to get the potato starch into the milk? Cook the potatoes in the milk.

The result is not only a perfect gratin, but a much faster one as well. By cooking the sliced potatoes in seasoned milk before turning them into a gratin dish, you achieve four-fold benefits. The potatoes cook much more quickly than they would in the oven and are seasoned more evenly, while the released potato starch prevents the milk proteins from clumping and separating. Meanwhile, the starch thickens the milk, yielding a creamy sauce. Depending on the thickness of the potato slices, the gratin can be finished in fewer than 20 minutes.

Perfect gratin.

Potato gratin

I’ve found that medium-starch potatoes retain their shape best but release enough starch that the slices cling together in a fairly thick cake bound in a creamy sauce. Yellow potatoes like Yukon Gold or Yellow Finn tend to be medium-starch, medium-moisture. “Waxy” potatoes, which tend to have red skins, don’t release enough starch for my taste, and starchy potatoes like Russets (the heart-shaped potato god depicted above) tend to break apart during cooking.

One more thing. I’ve read some crazy things about the French expression of potato gratin, pommes dauphinoise, including those that assert that the milk really is supposed to curdle (to approximate some sort of ersatz cheeselike state). No less an authority on gluttony than Jeffrey Steingarten has made this claim, which seems to me ridiculous. Why would the French bake potatoes in milk until it curdled? That seems to me contrary to anything the French would do. Now, some recipes for pommes dauphinoise call for cream – single (light) cream, half and half, or heavy cream – rather than milk, and that seems to me plausible, if kind of heavy. So if you like, feel free to substitute cream for some of the milk. But don’t let it curdle. The gratin should be smooth, with a fine, dense texture.

2 lbs (about four to six) medium-starch potatoes, such as Yellow Finn or Yukon gold, peeled
About one quart of milk (you probably will not use it all), or substitute up to 1 c cream for every 3 c milk
Leaves from three or four thyme branches
scant 1/2 tsp salt per pound of potatoes
One or two large garlic cloves
Optional: Parmigiano-Reggiano, grated
Oven 400F

Heat about ½ cup of the milk to about 120F and stir in the salt and the thyme. Ensure that the salt is dissolved and add to the rest of the cold milk or milk/cream mixture.

Using a mandoline or benriner, slice the potatoes thinly (you also may use a food processor) and add them all to a pot. Pour seasoned milk over just to cover, and place over medium low heat. Bring the entire pot to a simmer. Be careful not to let the milk boil, as it may curdle and will certainly boil over. If your potatoes are sliced very thinly (as they would be if you use a benriner or a mandoline set to 1/16”), the potatoes should be just tender virtually as soon as the milk simmers. If they are not just tender, simmer for another minute or two until they are tender.

Rub a large shallow gratin dish (or several small gratin dishes) with the garlic clove. Dispense with the painful layering process – gratin is, after all, a rustic dish – and pour the potatoes into the gratin dish, with milk to cover. Sprinkle with cheese, if you’re using it. Bake until bubbling and golden brown. Cool slightly. Don’t worry if the dish appears somewhat moist – the potatoes will absorb any remaining liquid, firming up and becoming thick and creamy.

Gratin.

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4 thoughts on “Gratinizing.

  1. This worked perfectly tonight! I went 50/50 on half-and-half and 1% milk (because that’s what I had on hand, but it made my head hurt to do the milkfat calculations, so I stopped). And I cheated on greasing the dish; I used garlic infused olive oil – just a bit rubbed on by hand. My son grated a little PR on top at the table, but I had mine without.

    Cook ’em in the milk. Brilliant!

  2. Excellent advice! I’ve tried potato gratin before and had
    the separate layers, the greasy runoff, all of the flaws you have
    now solved! I’m going to have to give your method a try. Love your
    blog!

  3. This is truly brilliant. I’ve always loved potato gratin but resisted serving it to guests because I never knew what kind of curdled or greasy mess I would end up with. Now, I think I could go for it!

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