First of all, yes I know a classic potatoes au gratin doesn't include roasted poblanos.
But I swear, everything else in this recipe is totally classic. It's just that I still have Mexico on the brain after our recent fabulous culinary immersion trip there. If you object to the poblano, just eliminate it without making any other changes.
Was it only a month ago we were packing to go on vacation?? It seems like the past 3 weeks have lasted at least 3 months. Is it like that for you too?
One thing I know, in these uncertain times when I'm daily hearing about challenges the world is going through, I need comfort food. Stat. And a classic potatoes au gratin is just about perfect.
The most common questions I see when making potatoes au gratin is what kind of potatoes to use, best cheeses, and “do you really have to use heavy cream?”. Let's take them one at a time.
Best Potatoes for Potatoes Au Gratin
The two most popular choices are russets and Yukon golds. The decision balances creaminess against the ability of the potatoes to hold their shape when baked. In the end it's up to you which is more important.
Russet potatoes have the highest starch content. They cook up less dense than Yukon golds, and don't hold their shape as well. And this is what's important for the ultimate creamy potatoes au gratin. Russets break down a little into the sauce, making it creamier. Just be sure not to over bake a gratin using russets, as they can become a little mushy.
Pro tip: Russet potatoes absorb more liquid than Yukon golds. The recipe below is written for Yukons. If you choose to go with russets, add an additional 1/2 cup of heavy cream. And be sure to re-balance the seasoning.
Yukon Gold potatoes are the next step down in starch content. They hold their shape very well, including when scooped out onto plates. Since they hold their shape and don't partially disintegrate into the cream, these gratins aren't quite as creamy – although I admit they're plenty creamy for me. Many people see Yukon golds as the best overall combination.
Pro-tip: If you want to amp up the creaminess of a gratin using Yukon golds, add 1 tablespoon all-purpose flour to the cream mixture on the stove. This will thicken the sauce a bit more. Another tip is to add several thin pats of butter between each layer of potatoes.
Best Cheeses for Potatoes Au Gratin
The traditional cheese used in potatoes au gratin is Gruyere. But feel free to mix it up with other cheeses, so long as they're good melting cheeses. I've used Monterey Jack Cheese with great success, and I've seen cheddar used as well.
I always like to add a little Parmigiano Reggiano cheese for a hint of sharpness to a cheesy creamy dish. If it's not available, you can use Pecorino Romano cheese instead.
Pro-tip: Grate your own cheese. Pre-grated cheese includes cellulose which prevents the cheese from caking together. It also dries the cheese out more, and mutes its flavor.
Do You Really Need To Use Heavy Cream?
No. The purpose of using heavy cream is to create a thick sauce. Heavy cream thickens with heat.
However, you can use whole or 2% milk. But you'll need to thicken it by making a roux with flour. If you follow the video, Use 2 tablespoons of butter and 2 tablespoons of all-purpose flour. Only complete the steps through adding the milk and thickening the sauce.
How To Build Flavor in a Potato Au Gratin
I've yet to meet a potato au gratin I haven't loved. But my favorites are ones with a lot of flavor in the sauce.
I do this a few ways:
- I add a scoop of Better Than Bouillion paste plus mustard to the cream and milk mixture on the stove.
- Next, I steep herbs, such as thyme, in the cream mixture. I've also used sage with great success, but because it's flavor it stronger, I don't need nearly as much.
- Finally, I reduce the cream mixture over a low simmer, and allow it to cool before removing the herbs from the pan. This intensifies the flavors and infuses the herbs just the right amount in the sauce.
- I've made the entire gratin ahead, except adding the breadcrumbs, and just reheated it for a party with great success. I add the breadcrumbs to the top when I rewarm the gratin. If you choose this make-ahead path, add an additional 1/4 cup of heavy cream to the pot when simmering with the herbs. The potatoes will absorb some of the liquid in the refrigerator, and otherwise the gratin will be a bit dry.
- Alternatively, you can make the gratin up to the point where you bake it off. Cover it, and place in the refrigerator. As a note, the baking time will be extended if you place the gratin in the oven while it's still cold, and I still recommend adding the extra 1/4 cup liquid to the cream sauce.
Classic Potatoes Au Gratin (with Poblanos)
- 2 tablespoons unsalted butter, room temperature, divided
- 1 medium shallot, peeled and thinly sliced
- 1 tablespoon garlic paste, or 3 garlic cloves, peeled, smashed and minced
- 2 cups heavy cream
- 1/2 cup whole milk
- 1 teaspoon Better Than Bouillon paste
- 1 teaspoon dijon mustard
- 1/2 teaspoon kosher salt, or 1/4 teaspoon table salt
- 1/4 teaspoon freshly ground black pepper
- 10 sprigs fresh thyme
- 1 poblano pepper
- 4 pounds Yukon potatoes, unpeeled
- 3 ounces grated Gruyère cheese, about 1 1/4 cup
- 1 ounce grated Parmeson, about 1/4 cup
- 2 tablespoons toasted breadcrumbs
- Preheat the oven to 350˚F. Smear 1/2 tablespoon butter all over the inside of a 9" X 13" baking dish. Set aside.
- Melt the remaining butter in a medium pot over medium heat. Add the sliced shallot and garlic and sauté for 5 minutes.
- Stir in the cream and milk. Add the bouillion, mustard, salt, pepper and thyme sprigs. Simmer for 15 - 20 minutes, until reduced by 1/4 cup. Let cool and remove the thyme.
- Roast the poblano pepper on a baking sheet under a broiler until the skin blisters, turning as needed. This should take about 15 minutes. Place in a jar or plastic bag. Seal and wait for 10 minutes. Remove the pepper and peel. Slice open, scrape out the seeds, and dice.
- Thinly slice the potatoes, approximately 1/8" thick. I use a hand-held mandolin, and set it on #2 setting.
- Arrange the potato slices like shingles on the bottom of the baking dish until the bottom is covered. Lightly salt and pepper the potatoes, and sprinkle 1/3 of the Gruyere cheese and 1/3 of the diced poblanos over the slices.
- Repeat for 2 more layers, finishing with the final 1/3 of the Gruyere and poblanos. Pour the cream reduction over the potatoes. Cover the baking dish tightly with foil. Bake for 60 - 75 minutes, until the potatoes are tender. If baking this at 5000-7000 feet, you may need to bake it for 75 - 85 minutes.
- Uncover, sprinkle with Parmesan and toasted breadcrumbs, if using. Bake for an additional 10 minutes.
- Serve piping hot.