Potatoes gratin is one of the world's best comfort foods, meaning they are absolutely irresistible and require hours of gym time to recover from. Still, these potatoes are too good to go without. Potatoes gratin is like a blank canvas. In their most purest form (potatoes, dairy, cheese, salt and pepper) they are exquisite.

World's best comfort food has lots of variations

While near perfect, basic potatoes gratin, is a great starting point for delicious variations. You can use a variety of cheeses and combinations of cheese. You can fatten them up with cream or take a more judicious approach with milk. You can layer with herbs, seasonings and sautéed vegetables. You can heat the milk or cream, or just dump the dairy on top of the potatoes. You can make beautiful concentric layers of potatoes and cheese, or just mix them up together. The best thing about potatoes gratin is you really can't screw them up.

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The zen of potatoes gratin -- analyzing the variables

Over the years, whenever I have made these potatoes I have done them differently. Finally I decided to analyze a number of recipes and figure out the zen of potatoes gratin. Here is the essence of my analysis:

Temperature and time

Most recipes call for temperatures between 350 and 400 degrees. The hotter the oven the shorter the cooking time. In a 350 degree oven plan to cook your potatoes for about an hour. In a 400 degree oven they should take 40-45 minutes.

Type of potatoes

You have three basic choices:  1) your basic russet, 2) any of the waxier potatoes (yukon gold, red, white or blue), or 3) sweet potatoes. The advantage of waxy potatoes over russets is the waxy potatoes don't fall apart as easily as the russets do. The advantage of russets over the waxy potatoes is russets absorb more of the creamy sauce. The advantage of the sweet potato is they are an excellent choice nutritionally and their natural sweetness takes a gratin in a unique direction. The bottom line, is you can't go wrong. All potatoes are good.

Yukon gold potatoes

Cutting your potatoes

The secret to a great gratin is slicing your potatoes thinly and uniformly. Your best bet is to use a mandolin and slice them in 1/8" slices. When layering your potatoes, save the most uniform pieces for the top layer. Use the weird, small and extra large pieces to create the first two layers and no one will know the difference. Take a little extra care on the last layer to artfully arrange uniform sized slices.

Mandolin makes slicing easy and uniform

Mandolin-sliced potatoes

Cheese

There are two things to consider regarding cheese and your gratin:

1)  What kind of cheese?

Again, there are no wrong answers here. Classically, gruyere and parmesan are traditional, but any single or combination of cheese is wonderful. Blue cheese and blue cheese combinations are great. Goat, cheddar and manchego are great. When in doubt use whatever you have on hand. Whatever cheese you choose, it is nice to finish your gratin with a couple tablespoons of grated parmesan to help brown the top layer.

2) How much cheese?

I analyzed the potato to cheese ratio of several recipes and found that most run between a 1/4 cup and 1/2 cup per pound of potatoes. I tend to lean towards the cheesier end of the spectrum.

Dairy

There are two decisions to be made regarding dairy:  type of dairy, and quantity:

1)  What kind of dairy?

Do you use milk or cream? After testing both, I have to say both are good, but in my opinion cream results in the best texture and taste. If you use milk, you need to add a tablespoon of butter to dot over each layer. No butter is needed if you use cream. I tested milk vs. cream on a dinner party of 8 and 75 % preferred the gratin made with cream. Cream gratin browns better and has a creamier more unctuous texture. You can also mix milk and cream or half-and-half and dial in the amount of cream you want to use. If you are adverse to cooking with cream, no problem, Your milk-based gratin will be wonderful.

Cream instead of milk results in better browning, flavor and texture

2) How much dairy?

In the recipes I analyzed, the ratio of potato to dairy ran from 1 pound of potatoes : 2/3 cup dairy, to 1 pound of potatoes : 1.75 cup dairy. To me, it is not so much the ratio of potatoes to dairy as the depth of the dairy compared to the depth of the potato in the pan. You want your potatoes to cook in the dairy and be fully absorbed by the end of the cooking process. When you pour in your dairy, it should come up two thirds of the way up the potatoes, but not cover them. For 2 pounds of potatoes in a 13 x 9 x 2" pan, you will need about 2.5 cups dairy. It is better to eyeball the depth than to follow a strict measurement.

Method

Some recipes call for bringing the dairy to a near boil before pouring it on the potatoes. Cooking the dairy is not necessary and just adds an additional step and an additional pan to clean. Just pour your milk or cream directly onto the layered potatoes and cheese.

Some recipes suggest you cover the potatoes, but I don't generally find this necessary.

One trick to insure your potatoes are all cooking evenly with your dairy is to remove them from the oven midway and press them down into the dairy with a spatula.

Other ingredients

You can flavor your gratins with herbs and spices, the most common being nutmeg, garlic, rosemary or thyme. You can slice other vegetables such as fennel, cauliflower, onion or turnip and layer them into the gratin with the potatoes. Or you can sauté spinach, kale, mushrooms and other vegetables and layer them between the potatoes and cheese.

Go wild or stick to the traditional, it is hard to go wrong with potatoes gratin, and easy to create something sublime. See my basic potatoes gratin recipe for a starting point.

Making ahead

Potatoes gratin are very durable. You can make ahead and then reheat in the oven at 350.

Tips

• If you have a food processor, use it to grate your cheese. It will save you time and knuckles.
• Use disposable foil pans to cook your gratin in. As delicious as these potatoes are, they make a mess of a baking pan. Skip the scrubbing and go disposable. You will NEVER hear me say that for anything but these potatoes.
• If you don't want to think about all these variables just follow my recipe for basic Potatoes Gratin or Potato Gratin with Mushrooms and Blue Cheese or Roasted Butternut Squash and Cauliflower Gratin or Beet and Kale Gratin. They are all delicious!
• Make double what you think you will need. Everyone will go for seconds.