Creamy Au Gratin Potatoes

Potatoes au gratin is like the French cousin of classic scalloped potatoes—with lots of cheese folded in. (Truth be told, the names are often used interchangeably.) In this dish, thin slices of Yukon gold potatoes are layered in a baking dish, smothered in a creamy sauce, and then baked until tender. The result is a melt-in-your mouth potato side that will become your go-to side dish for everything from holiday buffets to weeknight suppers.

Cheesy, creamy, and buttery, this is the potato side everyone will scoop up. It's great with just about any protein—chicken, ham, turkey, or even a steak.

But we'll be honest: Au gratin potatoes do require quite a bit of slicing. Still, it's worth it for layers of ooey-gooey goodness. Plus, it's a great excuse to break out the mandoline collecting dust in the cupboard. Just don't forget to use the hand guard.

Ingredients for Au Gratin Potatoes

The ingredient list for this recipe is fairly short and simple, but there are a few key ingredients that make this creamy potato side as delicious as it is.

• Butter: We call for unsalted by default, but if you only have salted, just scale back on how much salt you add so the final dish isn't overly salty.
• Garlic: This cooks down quite a lot but still manages to provide a backbone of flavor.
• Fresh thyme: With its subtle lemon flavor, fresh thyme adds a bit of brightness to this rich and creamy dish. It is commonly paired with potatoes, but also pairs well with most proteins, like chicken, fish, or pork. To easily remove the leaves from the stems, simply pinch the top of the sprig and slide your fingers down it to release the leaves. You can use dried thyme if you can't find it fresh, but use about half the amount, as dried thyme is much more potent. Other hearty fresh herbs like rosemary can be used in place of thyme, too.
• Heavy whipping cream: This is the bulk of the cream sauce. You could use whole milk, but the sauce will likely not thicken up as intended.
• Cornstarch and water: Speaking of thickening up, you'll make a cornstarch slurry to help the cream sauce along in its journey to being thick and rich.
• Yukon gold potatoes: Our Test Kitchen recommends using Yukon gold or gold potatoes for this au gratin potatoes recipe. Test Kitchen pro Amanda Stanfield says, "They work well because you eliminate having to peel them, and the starch content holds up well during the baking process and doesn't get as mushy as russet potatoes would."
• White Cheddar cheese: There is no difference in taste or texture between white Cheddar and orange Cheddar, but like orange Cheddar, white Cheddar comes in mild, medium, and sharp varieties. For this recipe we suggest a mild version and use white instead of orange because of how it blends seamlessly into the cream sauce.
• Parmesan: Adds nuttiness and a good hit of salt.
• Salt and black pepper: For seasoning. Taste and adjust according to your taste.

How To Make Au Gratin Potatoes

Just 30 minutes of hands-on cooking is needed to make au gratin potatoes. You can peel potatoes ahead of time if you want to break up recipe prep. Just takes steps to make sure the potatoes don't turn brown.

• Step 1. Make the sauce: Melt the butter in a medium saucepan over medium-high. Add garlic and thyme, and cook, stirring constantly, until fragrant. Mix in the cream, and season with salt. Reduce heat to low, and cook for another 5 minutes. Whisk together warm water and cornstarch in a small bowl. Stir the cornstarch mixture into the saucepan, and cook, whisking constantly, until thickened slightly. Whisk in Parmesan cheese and 1/2 cup of the Cheddar; cook, whisking often, until smooth and thickened, and then remove the sauce from the heat.
• Step 2. Assemble: Gently toss together potato slices, black pepper, and remaining salt in a medium bowl. Arrange slices in an even layer on the bottom of the baking dish. Repeat, creating layers with the remaining potatoes.
• Step 3. Bake: Pour the sauce evenly over the potatoes, and sprinkle with the remaining Cheddar. Bake until the potatoes are tender, and the top is golden brown, 50 minutes to 1 hour. Remove from the oven, and let stand for 15 minutes. Garnish with additional fresh thyme leaves.

Slicing Potatoes for Au Gratin Potatoes

Cutting potatoes 1/8-inch thick can be a little tricky, but it's important to get your potatoes that thin so that they cook properly. Here are a few potato-cutting tips:

1. Grab a sharp knife: Cutting potatoes this thin with a dull knife is a recipe for disaster. Make sure your knife is super sharp before you start, and make sure to tuck your finger tips in while slicing.
2. Better yet, grab a mandoline. As scary as they may seem, mandolines get clean, even, and most importantly very thin slices out of a potato. Once you know what you're doing, the mandoline is faster than slicing by hand, and unless you have rockstar knife skills, they will probably be more consistent slices, too. The key is using a hand guard or glove to protect your fingers, and apply even pressure. Just like slicing by hand, discard the end of the potato when it gets too small to avoid any injuries.
3. Keep a bowl of ice water nearby. Dropping the potato slices into a bowl of ice water while you prep will prevent the slices from oxidizing and turning brown. Strain and pat dry when ready to assemble the gratin.