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Ultra Cheesy Potato Gratin: The Perfect Vegetarian Side Dish

Chelsea Kram – XO&So: Vegetarian Comfort Food
Think of the cheesiest mac and cheese you've ever had but with potatoes instead of noodles and you get this ultra cheesy potato gratin recipe!
Prep Time 20 mins
Cook Time 1 hr 15 mins
Course Side Dish
Servings 4
Calories 898 kcal


  • 1 cup white onion finely diced
  • 2 cloves garlic minced
  • 3 tablespoon unsalted butter 42 g
  • 3 tablespoon all-purpose flour
  • ½ teaspoon mustard powder
  • ½ teaspoon garlic powder
  • ½ teaspoon onion powder
  • ½ teaspoon salt or more, to taste
  • black pepper to taste
  • 2 cups whipping cream
  • 1.5 cups sharp cheddar cheese shredded from a block, not pre-shredded
  • 900 g Yukon gold or russet potatoes about four large potatoes, sliced to ⅛ to ¼-inch thick with a mandolin
  • ¼ cup parmesan cheese optional, finely grated
  • parsley optional, for garnish


  • Heat your oven to 350 F. Grease an 8x8 dish and set aside.
  • Melt butter in a large skillet on medium heat WITH the diced onions and minced garlic.
    Once the butter is melted and the onions have softened, whisk in the flour, salt and pepper, mustard powder, onion powder, and garlic powder until it forms a paste. (This takes about one minute)
  • SLOWLY add the cream to the mixture a bit at a time. Keep whisking as you add the cream. It will thicken up as you go. Spend at least five minutes on this. 
  • Once all of the cream is added, turn the heat to low and add the freshly shredded cheese into the mixture. Let the heat of the roux begin to melt the cheese.*
    Once the cheese is melted and your sauce is done, remove from heat and set aside.
  • Wash, dry, and peel your potatoes. Slice your potatoes into slices between ⅛ and ¼-inch thick.**
    Add your sliced potatoes to a large bowl. Toss with additional salt and pepper, to taste.
  • Add half of the sliced potatoes to the greased dish, laying as flat as possible. Top with half of the cheese sauce. 
    Now add the rest of the potatoes on top, keeping them as flat as possible. Top with the rest of the cheese sauce.
  • Cover the dish with tin foil and bake for 60 minutes.
    Remove the tin foil and add the shredded parmesan (if using).
    Cook for another 15 minutes, or until bubbly and golden. You can test the potatoes with a fork and make sure a fork goes in easily.
  • Let the potato gratin stand for at least 15 minutes before serving – it will be hot! Top with fresh or dried parsley for garnish.


*Don't stir the cheese sauce too much or it will get stringy. 
**If they're not thin enough, they won't cook in time. I definitely recommend using a mandolin slicer. 
Leftovers store well in the fridge for up to five days. They reheat well, it just won't be quite as saucy as when they're first made!
You could double this recipe and bake it in a 9 x 13 dish. 


Calories: 898kcalCarbohydrates: 52gProtein: 21gFat: 69gSaturated Fat: 43gCholesterol: 235mgSodium: 716mgPotassium: 1136mgFiber: 6gSugar: 4gVitamin A: 2489IUVitamin C: 48mgCalcium: 498mgIron: 2mg
Keyword cheesy, holiday, potatoes
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