Sweet Potato Gratin

Isabella

This Sweet Potato Gratin takes comfort food to an entirely new level with layers of tender sweet potatoes baked in a creamy, herb-infused sauce, finished with bubbling Gruyère and Parmesan cheese. Elegant enough for the holidays yet simple enough for a cozy weeknight dinner, it’s a stunning, crowd-pleasing dish that delivers sweet, savory, and nutty perfection.

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Prep Time 25

Cook Time 1

Total Time 1 25

Servings: 6 servings

Course: Dinner, Holiday, Side Dish

Cuisine: American, French-inspired

Calories: 360

Ingredients Method Notes

Ingredients

For the Creamy Herb Sauce

3 tbsp unsalted butter, divided (plus extra for greasing foil and dish)
4 cloves garlic, finely chopped
2 tbsp fresh thyme leaves, chopped (plus more for garnish)
1 tbsp fresh sage leaves, chopped
1 cup heavy cream
0.75 cup whole milk
0.25 tsp ground cinnamon
0.25 tsp ground nutmeg
Kosher salt and freshly ground black pepper, to taste

For the Egg-Cheese Mixture

2 large eggs, room temperature
0.75 cup grated Parmesan cheese, divided

For Layering

2 lb sweet potatoes (a mix of purple, orange, and white), peeled and thinly sliced (about ⅛ inch thick)
2.67 cups shredded Gruyère cheese, divided

Method

Step 1: Prepare the Dish and Infuse the Cream
Preheat the oven to 375°F (190°C) and butter a 2-quart casserole dish. In a small saucepan, melt 2 tablespoons of butter. Add chopped garlic and sauté for 30 seconds. Stir in thyme, sage, and ½ teaspoon salt, cooking briefly. Add cream, milk, cinnamon, and nutmeg, bringing to a gentle simmer for 5 minutes before removing from heat.
Step 2: Temper the Eggs
In a bowl, lightly beat the eggs. Slowly whisk in 1 cup of the warm cream mixture to temper, then return the mixture to the saucepan. Add ½ cup Parmesan, season with black pepper, and stir until smooth.
Step 3: Assemble the Layers
Layer sweet potato slices in the prepared dish, overlapping slightly. Sprinkle with salt, top with Gruyère and cream mixture. Repeat 3 more times, finishing with the cream. Sprinkle the remaining Parmesan on top.
Step 4: Bake Until Golden
Cover with buttered foil and bake for 30 minutes. Remove foil and bake another 30 minutes, until bubbling and golden. Garnish with fresh thyme before serving.

Notes

For best results, slice potatoes evenly with a mandoline. Mix different sweet potato colors for a vibrant look. Substitute Gruyère with Comté or Fontina for variation. Assemble a day ahead and refrigerate if needed. Broil briefly for an extra golden top.