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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin with thinly sliced Yukon gold, sweet potato, and parsnip layered and baked until bubbling and golden. Warm cream, garlic, thyme, and nutmeg soak into the vegetables for a creamy, fork-tender texture under a Gruyere-Parmesan crust.
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Prep Time 25 minutes
Cook Time 1 hour 10 minutes
Rest 10 minutes
Total Time 1 hour 45 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French-inspired
Calories: 740
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 and heat the cream
  1. Preheat the oven to 375F, then butter a 9x13-inch baking dish. Keep the dish ready so the layers go in quickly.
  2. Warm the heavy cream, whole milk, garlic, fresh thyme leaves, salt, black pepper, and nutmeg until steaming, then remove from heat. You should see steam rising from the mixture but it should not be vigorously boiling.
Layer and bake
  1. Layer a third of the Yukon gold potatoes, sweet potatoes, and parsnips in the dish, then top with a third of the Gruyere. Spread the vegetables evenly so the gratin bakes uniformly.
  2. Repeat the layers twice more, ending with a layer topped with Gruyere. Aim for tidy, even stacks for consistent tenderness.
  3. Pour the warm cream mixture evenly over the top. Make sure most of the surface is moistened, including edges.
  4. Cover with foil and bake for 45 minutes at 375F. Look for the sides to look set and the center to bubble lightly under the foil.
  5. Uncover, sprinkle with Parmesan, and bake 20-25 minutes at 375F until bubbly, golden, and fork-tender. The top should be crisp at the edges and the vegetables should slide off a fork.
Rest and serve
  1. Rest the gratin for 10 minutes before serving. This helps the creamy layers firm up so each scoop holds together.

Notes

Pro tip: slice the vegetables very thin and similar in thickness so they finish baking at the same time. Refrigerate leftovers in an airtight container for up to 3 days; reheat in a 350F oven until warmed through. Freezing is not recommended because the cream can separate when thawed. For a lighter option, replace half the heavy cream with more whole milk to reduce richness while keeping the same layering and bake times.