Au Gratin Potatoes

These creamy Au Gratin Potatoes is an easy side dish recipe that's make-ahead friendly and pairs well with just about anything! Classic ingredients include cream, Gruyere, Parmesan, thyme, fresh garlic, and more!

Prep Time20

Cook Time2

Total Time2 20

Course: Side Dish

Cuisine: American, French

Servings: people

Calories: 355kcal

Author: Stephanie

Ingredients

1 small yellow onion finely diced
3 tablespoons salted butter
4 cloves fresh garlic minced
2 teaspoons fresh thyme leaves
2 cups heavy cream
½ cup milk
2 cups shredded gruyere cheese
½ cup grated Parmesan cheese
¼ teaspoon EACH: Salt, pepper
2 ½ lbs. russet potatoes
Chives to garnish

US Customary - Metric

Instructions

Preheat oven to 350°F. This can be done in step 4 after the onions are caramelized as well.
Combine the heavy cream and milk in a medium measuring cup with a spout. Temper in the microwave for 1 minute, then set aside.
Add the diced onions and butter to a soup pot over medium heat. Soften for 10 minutes, stirring often. Reduce heat to medium-low and cook for 10-15 more minutes, stirring frequently, until they begin to brown and caramelize slightly. Add the garlic and thyme and cook for 2 minutes.
Turn heat off and let the pot cool for 1 minute. Gradually stir in the heavy cream/milk. Set the heat to medium-high and bring the liquid to a boil, then remove from heat.
Gradually stir in the gruyere and Parmesan cheese, giving it a chance to melt as it's added a little at a time. Stir in the salt and pepper.
Cut the potatoes into 1/8-inch thick slices, no thicker or they won’t cook through. A mandoline slicer makes this much easier.
Arrange 1/3 of the potatoes on the bottom of a lightly greased baking dish. (Mine is 2.5 quarts. A 9 x 13-inch baking dish also works.) Pro Tip: Lightly sprinkle each layer of the potatoes with a little salt.
Add 1/3 of the sauce over the potatoes. Repeat two more times: (Potatoes, sauce. Potatoes, sauce).
Cover and bake for 1 hour.
Uncover and bake for 30 minutes. Optional: Broil at 425°F for 1-2 minutes to add more color to the top if desired. Watch it carefully during this time.
Remove from the oven and let it rest for 5-10 minutes prior to serving. Garnish with chives and serve!

Notes

Pro Tips:

Potatoes: Use russets! They have a high starch content which thickens the sauce as they cook. They also absorb the sauce during cooking which is necessary- it makes them more flavorful and there is plenty of sauce to be absorbed. Yukon Golds are the next best option. Avoid waxy potatoes like red potatoes, they won't absorb or thicken the sauce.
Slice the potatoes thin: I'd almost call them paper thin (1/8th of an inch). This ensures they cook through all the way through.
Use a Mandoline: This is the quickest and most accurate way to get thin, even slices. Use it with caution:Use every safety measure and safety tool provided and then some. They are very sharp and it's easy to cut your fingers. (Trust me.)
Cheese: a 6 oz. block of Gruyere is enough to make 2 cups shredded. (I use 5.5 oz. of the block) I use Emmi Le Gruyère Cheese and Belgioioso Parmesan. Fontina Cheese makes a great addition to this as well. Cheddar can be used if needed, but I'd recommend Gruyere if at all possible.
Shred/Grate the cheese from a block. Don't use packaged shredded/grated cheese as it won't melt as well or taste as good.
Garlic- Definitely use fresh cloves for this recipe (vs. jarred).
Sauce: Keep two things in mind: 1.) It's thin at first, but thickens more and more as the dish cooks. 2.) There is a lot of it, but the potatoes continue to absorb it during cooking, and some of it evaporates when it's cooked without the cover.

Make-Ahead Method:

Assemble as outlined and bake at 350° for 45 minutes. Let it cool completely, then cover and refrigerate for up to 2 days. (It will be very saucy and still on the thin side.)
When ready to serve: Let it sit out at room temperature for 1 hour. Bake covered at 350° for 20 minutes. Remove cover and bake for 30 more minutes, or until bubbly and hot. Broil for 1 minute at the end if desired.

Storage:

Store in an airtight container and refrigerate for up to 5 days. While leftovers can be frozen, they don't reheat exactly back to their original consistency.

Nutritional information is an estimate and is per serving. This recipe makes 12 servings.

Nutrition