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Sweet Potato & Cranberry Gratin

An elegant and savory-sweet gratin featuring thinly sliced sweet potatoes layered with a creamy, herbed sauce, tart cranberries, and a golden-brown cheesy crust.
Print Recipe
Prep Time 20 minutes
Cook Time 1 hour 15 minutes
Total Time 1 hour 35 minutes
Servings: 8 servings
Course: Holiday, Side Dish
Cuisine: American, French
Calories: 480
Ingredients Equipment Method Notes

Ingredients
  

  • 4 medium-large sweet potatoes about 3 lbs, peeled and thinly sliced
  • 2 tbsp unsalted butter
  • 2 cloves garlic minced
  • 2 tbsp all-purpose flour
  • 2 cups heavy cream
  • 1 cup whole milk
  • 1 tsp fresh rosemary minced, plus sprigs for garnish
  • 0.5 tsp salt or to taste
  • 0.25 tsp freshly ground black pepper or to taste
  • pinch nutmeg optional
  • 1 cup fresh or frozen cranberries
  • 2 tbsp light brown sugar packed
  • 1 cup Gruyère cheese freshly shredded

Equipment

  • 9x13 inch baking dish
  • Mandoline slicer (recommended)
  • Medium saucepan
  • Whisk

Method
 

  1. Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
  2. Melt butter in a saucepan over medium heat. Sauté minced garlic for 1 minute. Whisk in flour for 1-2 minutes.
  3. Gradually whisk in heavy cream and milk until smooth and thickened. Remove from heat. Stir in rosemary, salt, pepper, and nutmeg.
  4. Pour ⅓ of the cream sauce into the prepared dish. Layer half of the sweet potatoes, then half of the cranberries, then ⅓ of the Gruyère cheese. Drizzle with another ⅓ of the sauce.
  5. Repeat with remaining sweet potatoes, cranberries, another ⅓ of the Gruyère, and the remaining sauce.
  6. Sprinkle the remaining Gruyère cheese over the top, then scatter the brown sugar evenly over the cheese.
  7. Cover with foil and bake for 45-60 minutes, until sweet potatoes are tender.
  8. Remove foil. Increase oven to 400°F (200°C). Bake for another 15-20 minutes, until top is golden brown and bubbly.
  9. Let rest for 10-15 minutes before serving. Garnish with fresh rosemary sprigs.

Notes

Thinly slicing sweet potatoes is key for even cooking. A mandoline is highly recommended. For make-ahead, assemble up to 24 hours in advance, cover, and refrigerate. Add 10-15 minutes to covered baking time if baking from cold.