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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin with thin-sliced Yukon gold potatoes, sweet potatoes, and parsnips baked until fork-tender under a bubbling Gruyere-Parmesan crust. French-inspired layering plus a steaming cream-garlic thyme mixture creates a creamy, browned top.
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Prep Time 25 minutes
Cook Time 1 hour 10 minutes
resting 10 minutes
Total Time 1 hour 45 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French-inspired
Calories: 545
Ingredients Equipment Method Notes

Ingredients
  

Yukon gold potatoes
  • 1 lb Yukon gold potatoes peeled and thinly sliced
Sweet potatoes
  • 1 lb sweet potatoes peeled and thinly sliced
Parsnips
  • 2 parsnips peeled and thinly sliced
Cream mixture
  • 1.5 cup heavy cream
  • 0.5 cup whole milk
  • 3 clove garlic minced
  • 1 tsp fresh thyme leaves
  • 1.5 tsp salt
  • 0.5 tsp black pepper
  • 0.25 tsp nutmeg
Cheese
  • 2 cup shredded Gruyere divided
  • 0.5 cup grated Parmesan

Equipment

  • 1 sheet pan
  • 1 Dutch oven

Method
 

Prep and heat
  1. Preheat the oven to 375°F and butter a 9x13-inch baking dish.
  2. Warm the heavy cream, whole milk, minced garlic, thyme leaves, salt, black pepper, and nutmeg just until steaming, then remove from heat.
Layer and bake
  1. Layer one third of the Yukon gold potatoes, sweet potatoes, and parsnips in the dish, then top with one third of the shredded Gruyere.
  2. Repeat the layers twice, then pour the warm cream mixture evenly over the top.
  3. Cover the dish with foil and bake for 45 minutes at 375°F.
Brown the top and finish
  1. Uncover the gratin, sprinkle with the grated Parmesan, and bake 20 to 25 minutes at 375°F until bubbly, golden, and fork-tender.
  2. Rest for 10 minutes before serving so the layers set and the sauce thickens.

Notes

For the creamiest texture, slice the potatoes and parsnips very thin and evenly so they finish at the same time; if your top browns too quickly near the end, loosely re-cover with foil. Store covered in the refrigerator up to 4 days; reheat in a 325°F oven until warmed through. Freezing is not recommended because the dairy can separate after thawing. For a lower-fat option, use half-and-half instead of heavy cream and reduce baking liquid browning by keeping the oven closer to the low end of the range.