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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin with thinly sliced potato, parsnip, carrot, and turnip baked until tender and topped with a golden, bubbling Gruyère-Parmesan crust. A classic French-American style gratin baked in a buttered 9x13 dish with a creamy garlic-thyme custard.
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Prep Time 25 minutes
Cook Time 1 hour
rest 10 minutes
Total Time 1 hour 35 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French-American
Calories: 610
Ingredients Equipment Method Notes

Ingredients
  

potatoes
  • 2 lb Yukon gold potatoes peeled and thinly sliced
parsnips
  • 2 parsnips peeled and thinly sliced
carrots
  • 3 carrots peeled and thinly sliced
turnip or celery root
  • 1 turnip or celery root large; peeled and thinly sliced
garlic
  • 4 cloves garlic minced
cream
  • 2 cup heavy cream
milk
  • 1 cup whole milk
thyme
  • 2 tsp fresh thyme
nutmeg
  • 0.25 tsp nutmeg
gruyere
  • 2 cup Gruyere cheese, shredded
parmesan
  • 0.5 cup parmesan, grated
butter
  • 3 tbsp unsalted butter
salt and pepper
  • 1 Salt and pepper to taste

Equipment

  • 1 sheet pan

Method
 

Prep the dish and aromatics
  1. Preheat oven to 375F. Butter a 9x13 baking dish generously so the gratin releases cleanly.
  2. Whisk heavy cream, whole milk, garlic, fresh thyme, nutmeg, and 1 teaspoon salt with pepper together until well combined. The mixture should look smooth and lightly speckled.
Layer and bake
  1. Layer Yukon gold potatoes, parsnips, carrots, and turnip or celery root in the dish, alternating types in slightly overlapping rows. Keep the slices even so they cook through at the same pace.
  2. Pour the cream mixture over the vegetables and press down gently to help it settle. Stop when most of the surface looks glossy and moistened.
  3. Cover tightly with foil and bake 40 minutes at 375F. Use the foil to trap steam and soften the root vegetables.
Broil-style finish and rest
  1. Uncover the dish and scatter Gruyere and parmesan over the top. Aim for an even layer so the crust browns in spots.
  2. Bake 20-25 more minutes at 375F until the vegetables are completely tender and the top is golden and bubbly. Look for active bubbling at the edges and slight browning on the cheese.
  3. Rest 10 minutes before serving. Letting it stand helps the creamy layers set for clean slices.

Notes

For best texture, slice the potatoes and other roots thin and consistent so they finish tender at the same time. Store leftovers covered in the refrigerator up to 3 days; reheat in the oven at 350F until warmed through. Freezing is not recommended because the creamy custard can separate when thawed. If you want a lighter option, use half-and-half instead of heavy cream (still add whole milk) for a slightly less rich gratin.