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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin with thin potato, sweet potato, and parsnip slices baked until tender and topped with a bubbling Gruyère crust. Warm cream, garlic, thyme, and Gruyère create a creamy layer that turns golden after uncovering.
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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: 630
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 garlic cloves, 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 cheese
  • 2 cup Gruyere cheese shredded, divided
Parmesan
  • 0.5 cup Parmesan grated

Equipment

  • 1 sheet pan

Method
 

Prep and preheat
  1. Preheat oven to 375F and butter a 9x13-inch baking dish.
Make the creamy base
  1. Warm heavy cream, whole milk, garlic, fresh thyme leaves, salt, black pepper, and nutmeg over heat until steaming, then remove from heat.
Layer the vegetables
  1. Layer a third of the Yukon gold potatoes, sweet potatoes, and parsnips in the dish, then top with a third of the Gruyere cheese.
  2. Repeat the layers twice so the vegetables and Gruyere cheese are used up.
  3. Pour the warm cream mixture evenly over the top until it settles between the slices.
Bake and brown
  1. Cover with foil and bake for 45 minutes until the vegetables are starting to soften at the edges.
  2. Uncover, sprinkle with Parmesan, and bake 20-25 minutes until bubbly, golden, and fork-tender.
Rest and serve
  1. Rest the gratin for 10 minutes before serving so the cream sets and slices hold together.

Notes

For the creamiest texture, use thin slices so the vegetables cook through in the same time window; aim for even thickness across potatoes, sweet potatoes, and parsnips. Store leftovers covered in the refrigerator for up to 4 days. Reheating in a 350F oven helps the top re-bubble. Freezing is not recommended because the cream can separate when thawed. If you want a lighter version, swap whole milk for half-and-half in the cream mixture to reduce richness while keeping it silky.