Au Gratin Potatoes start with thinly sliced golden potatoes that we layer in a luxuriously creamy and ultra-cheesy sauce. This deeply savory potato side-dish is sure to be a hit anywhere it's served!
Course Appetizer, Side Dish
Cuisine American, Vegetarian
Keyword au gratin potatoes, au gratin potatoes recipe, potatoes au gratin
PREP: Preheat oven to 350 degrees F. Generously grease a 9x9-inch (or 2-quart) pan with cooking spray and set aside.
PREP POTATOES: Peel and thinly slice potatoes (1/8th-inch thick). (I like to use a mandolin slicer for speed and accuracy.) Tightly pack potatoes in measuring cups to ensure a full 6 cups.
SAUCE: In a large nonstick pot, melt butter over low heat. Once melted, add garlic. Sauté 1 minute or until fragrant. Sprinkle in flour and whisk constantly for 1 minute until smooth (don't let it brown). Very gradually pour in 1 cup milk while whisking constantly. Once completely smooth, increase heat to medium-high and gradually add in the other cup of milk. Stir occasionally until mixture comes to a boil. Season to taste (I add 1-1/2 tsp salt & 1/4 tsp pepper).
SAUCE, CONT.: Once boiling, reduce the heat to medium-low and stir constantly for 2 minutes or until mixture is nicely thickened (Note 4). Remove pot from heat and let cool for 2 minutes. Stir in Cheddar cheese, mixing gently until melted and smooth. Add in the prepared potatoes and stir to coat.
ASSEMBLE: Add 1/3 of the potatoes to prepared pan. Sprinkle with 1/2 cup Gruyere cheese and 1/3 of the fresh thyme leaves. Add another 1/3 of potatoes on top and sprinkle with remaining 1/2 cup Gruyere cheese and 1/3 of fresh thyme leaves. Add remaining potatoes and then remaining thyme.
BAKE: Cover pan with foil and bake for 1 hour 15 minutes. Remove foil and use a table knife to pierce the middle of the pan to test if the potatoes are tender. (If not, bake a few more minutes and check again.) Sprinkle 1/2 cup Parmesan cheese on top and bake for another 10-15 minutes or until golden and bubbly. Optional: Broil for 1 minute at the end. Remove and let stand for 5-10 minutes before serving (sauce will thicken as it stands!) Enjoy!
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Notes
Note 1: Potatoes: Yukon gold (also called gold, Yukon, or yellow potatoes) are our hands-down favorite potato to use. Russet potatoes will also work. Peel potatoes, rinse in cool water then use a Mandoline slicer set at 1/8th-inch thickness to cut the potatoes and measure to get 6 packed full cups. Note 2: Milk: We like whole milk best; it delivers the richest end result. 2% and 1% will work, but we do not recommend skim milk or plant-based milk alternatives.Note 3:Parmesan: Packaged grated Parmesan (in the can) is very salty and won't melt as nicely in this recipe. We highly recommend grating a block of Parmesan cheese on the small holes of the grater for ultra-fine cheese shreds. Alternatively, use finely grated Parmesan cheese.Note 4: Thickness check: The sauce should be thick enough to coat the back of a wooden spoon. Lift up the spoon and immediately trace a line across the back of the spoon with your fingertip. If the line retains a clear track, the sauce is thick enough. If not, the sauce needs to be cooked a bit longer.