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Cheesy Root Vegetable Gratin

Cheesy root vegetable gratin with thinly sliced potatoes, parsnip, carrot, and turnip baked in a garlic-thyme cream sauce until tender. Finished with a golden, bubbling Gruyère and parmesan crust.
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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
  

potatoes
  • 2 lb Yukon gold potatoes peeled and thinly sliced
parsnips
  • 2 parsnips medium, peeled and thinly sliced
carrots
  • 3 carrots peeled and thinly sliced
turnip
  • 1 turnip or celery root large, peeled and thinly sliced
garlic
  • 4 garlic cloves, minced
cream and milk
  • 2 cup heavy cream
  • 1 cup whole milk
thyme and spice
  • 2 tsp fresh thyme
  • 0.25 tsp nutmeg
cheese
  • 2 cup Gruyere cheese shredded
  • 0.5 cup parmesan grated
butter
  • 3 tbsp unsalted butter for greasing
seasoning
  • 0.25 salt and pepper to taste; about 1 tsp salt for the cream mixture plus more as needed

Equipment

  • 1 sheet pan

Method
 

Prep and preheat
  1. Preheat the oven to 375F, then generously butter a 9x13 baking dish.
  2. Whisk heavy cream, whole milk, minced garlic, fresh thyme, nutmeg, salt, and pepper together until smooth.
Layer and bake
  1. Layer the root vegetables in the dish, alternating types in slightly overlapping rows.
  2. Pour the cream mixture over the vegetables, then press down gently so the slices settle.
  3. Cover tightly with foil and bake at 375F for 40 minutes, until the vegetables start to soften.
  4. Uncover and scatter the Gruyere and parmesan over the top so it forms a full, even layer.
  5. Bake 20-25 minutes more at 375F until the vegetables are completely tender and the top is golden and bubbly.
Rest and serve
  1. Rest the gratin for 10 minutes before serving so the sauce thickens slightly and the layers set.

Notes

For clean slices and even cooking, aim for uniformly thin rounds (use a mandoline if you have one). Refrigerate leftovers in an airtight container for up to 3 days; reheat covered in a 325F oven until hot throughout. Freezing is not recommended because cream-based gratins can break after thawing. For a dairy-light swap, use half-and-half for the cream and a plant-based cheese blend that melts, keeping the bake times similar.