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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin is French-inspired comfort with thinly sliced Yukon gold potato, sweet potato, and parsnip baked in a creamy garlic-thyme sauce under a bubbly Gruyere crust. Layering the vegetables and pouring the warm cream mixture helps everything cook evenly into tender, golden fork-tender slices.
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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: 540
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
heavy cream
  • 1.5 cup heavy cream
whole milk
  • 0.5 cup whole milk
garlic
  • 3 clove garlic minced
fresh thyme leaves
  • 1 tsp fresh thyme leaves
salt
  • 1.5 tsp salt
black pepper
  • 0.5 tsp black pepper
nutmeg
  • 0.25 tsp nutmeg
Gruyere
  • 2 cup Gruyere shredded, divided
Parmesan
  • 0.5 cup Parmesan grated

Equipment

  • 1 sheet pan

Method
 

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

Notes

For the creamiest texture, aim for uniformly thin vegetable slices so they cook at the same rate. Refrigerate leftovers in an airtight container up to 3 days; reheat covered at 325F until hot. Freezing is not recommended because the cream sauce may break when thawed. For a lighter option, use half-and-half instead of heavy cream (expect a slightly less rich, looser gratin).