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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin with thin-sliced Yukon gold potatoes, parsnip, carrot, and turnip baked in a creamy garlic-thyme sauce. Finished with a golden, bubbling Gruyere and parmesan crust, then rested for clean, sliceable layers.
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Prep Time 25 minutes
Cook Time 1 hour
resting 10 minutes
Total Time 1 hour 35 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French-American
Calories: 520
Ingredients Equipment Method Notes

Ingredients
  

Yukon gold 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 peeled and thinly sliced
garlic
  • 4 garlic cloves, minced
heavy cream
  • 2 cup heavy cream
whole milk
  • 1 cup whole milk
fresh thyme
  • 2 tsp fresh thyme
nutmeg
  • 0.25 tsp nutmeg
Gruyere cheese
  • 2 cup Gruyere cheese shredded
parmesan
  • 0.5 cup parmesan grated
unsalted butter
  • 3 tbsp unsalted butter
salt
  • 1 salt to taste
pepper
  • 1 pepper to taste

Equipment

  • 1 sheet pan

Method
 

Prep and heat
  1. Preheat the oven to 375°F. Butter a 9x13 baking dish generously with the unsalted butter so the gratin releases cleanly.
  2. Whisk heavy cream, whole milk, minced garlic, fresh thyme, nutmeg, 1 teaspoon salt, and pepper together until smooth. The mixture should look lightly speckled from the thyme.
Layer and bake covered
  1. Layer the root vegetables in the dish, alternating types in slightly overlapping rows. Press the slices down lightly so the layers stay compact.
  2. Pour the cream mixture over the vegetables, then press down gently again to encourage even soaking. Make sure most slices are moistened but not floating.
  3. Cover tightly with foil and bake at 375°F for 40 minutes. You should see steam and bubbling around the edges through the foil.
Finish with cheese and rest
  1. Uncover and scatter Gruyere and parmesan over the top in an even layer. The surface should be fully covered for a browned crust.
  2. Bake uncovered at 375°F for 20-25 minutes until the vegetables are completely tender and the top is golden and bubbly. Look for active bubbling and browned cheese at the edges.
  3. Rest the gratin for 10 minutes before serving. It will thicken slightly so the layers hold together when you scoop.

Notes

For the best texture, slice the potatoes and other roots as consistently thin as possible so everything finishes tender at the same time. Store leftovers covered in the refrigerator for up to 4 days and reheat in the oven or microwave. Freezing is not ideal because the cream can break and the vegetables may soften further. If you want a lighter option, use half-and-half instead of heavy cream for a slightly less rich gratin.