Before planning the menu for a recent chilly-weather meal for friends, I asked everyone if there were any particular dishes they were craving. Only one of them spoke up, with hopeful wishes for his favorite: "That creamy French potato thing with cheese on top."
There are a lot of French ways how to make au gratin potatoes (aka potatoes au gratin, or pommes de terre gratinées), many of them involving thinly sliced potatoes, butter, and cream. But a gratin doesn't have to be a potato dish. "Au gratin" is the French term for topping a dish with butter, bread crumbs, or cheese (or a mix of some or all three) and baking or broiling it until the topping is browned and crisp.
You can make gratin with almost any kind of vegetable or potato. Mushrooms, tomatoes, fennel, broccoli, collard greens, etc. But what my friend wanted, and what I'm here to tell you about today, is the kind of gratin that features layers of thinly sliced potatoes or root vegetables.
Since I aim to please, but also to teach, I promised I would make a gratin only if he'd help me so he could learn how to make his favorite for himself.
As we sliced potatoes and simmered cream, I remembered just how loose, adaptable, and totally doable this "fancy French" dish can be. It takes some time—longer than you might think—to bake in the oven, but other than that it's much easier than my friend thought it would be. And after all, that's what chilly weekends are for: puttering and chatting in the kitchen with a friend while a gratin slowly bubbles in the oven.
I can't be there to show you myself, so let me explain how to make au gratin potatoes this chilly weekend. Just follow these steps and you're on your way to this cozy, creamy, soul-warming dish. Heck, you can even make it the main event of your meal—it's certainly filling enough!
1. Get the oven and a baking dish ready
Turn your oven on to 350°F. Now pick a shallow baking or casserole dish: the size will depend on how many people you're feeding. I have a little gratin dish that makes just enough for two that I love to use sometimes. Whatever size you want to use, rub the inside with some butter. For extra garlic flavor, you can rub the inside of the dish with a split garlic clove before adding the butter.
2. Simmer and infuse cream
Pour some heavy cream into a small saucepan: you can eyeball this, but in general you'll need about 1/4 cup of cream per person you're serving. If you're unsure how much cream you'll need though, it's better to air on the side of too much here.
Now add some aromatics ingredients to the pot to infuse it with flavor. The simplest (and most classic) option is just a couple crushed garlic cloves, followed perhaps by a whisper of freshly grated nutmeg. Thyme, rosemary, or sage are all good options, or you could get spicy with a chili pepper or some crushed cardamom pods or cinnamon sticks. Mix and match to your hearts content, then bring the cream with your aromatic ingredients in it just to a boil, turn it off, cover the pot and let it sit while you prep the remaining ingredients. A small sprinkle of cayenne can help punch up the flavors if needed. And don't forget to add some salt.
3. Slice your root vegetables
While the cream infuses, slice up whatever root vegetables you want to use: Potatoes, sweet potatoes, celery root, turnips, parsnips, butternut squash—all good. Stick with one, or go for a mix. I love to do a mix of russet potatoes and celery root this time of year. No need to peel your potatoes (but you will want to peel that celery root), just slice them as thin as you possibly can. Use a mandolin if you have one, or the slicing blade of a food processor, or simply an old fashioned knife.
4. Add green things or onions, but cook them first
I love to sauté some sliced leeks until tender and add them to the mix of sliced root vegetables. Onions work too if you like. Or, steam or sauté your favorite hearty green (kale, collards, or swiss chard) with or without some onions or leeks. Set the cooked greens aside to layer into your gratin to make this decadent dish a little healthier.
5. Layer into a baking dish
If you're just using sliced root vegetables, start layering them in your buttered baking dish, stopping every few layers to sprinkle with salt and pepper and pour in some of your infused cream (pull the aromatics out, or just make sure not to pour them into your dish). Add some sautéed onions or leeks, or layers of greens if you're doing that. Repeat.
Keep layering until the dish is full, then pour in enough cream so that the liquid comes 3/4 of the way up the side of the vegetables. You might have leftover cream—reserve it for another use.
6. Top with cheese, or breadcrumbs, or butter, or both
Now, to get that official "au gratin" topping, you need to top the dish with something that will brown nicely in the oven. You can simply dot it with butter, or sprinkle it with breadcrumbs (and a bit of butter here too if you like) or—my favorite—pile it with shredded cheese. I like to use Gruyere, but any kind of meltable cheese will do. Add some grated Parmesan into whatever cheese you're using for extra flavor if you like.
7. Bake the gratin until tender and golden brown
Cover the whole dish tightly in foil, then set it on a rimmed baking sheet to catch drips just in case it starts dripping. Put it in your preheated oven, and bake until the root vegetables are crisp-tender when poked with a fork, about one hour. Uncover the dish, then continue baking until completely tender and golden-brown on top, another half hour or so.
If your vegetables are all tender but the top hasn't browned enough, turn on the broiler and give it a blast until it's nicely browned. Let it sit a bit to cool before serving so no one burns their tongues. Or, to make it in advance, let it come to room temperature and then reheat it in a 300°F oven for about 20 minutes until warmed through.
Do you like your potatoes crispy instead of creamy? Here's the dish for you:
