Description
A creamy and savory Sweet Potato Gratin featuring thinly sliced sweet potatoes layered with a fragrant garlic-onion cream sauce, fresh rosemary, and Parmesan cheese, baked to golden perfection. This comforting side dish combines tender sweet potatoes with a rich, cheesy sauce, perfect for holiday dinners or cozy weeknight meals.
Ingredients
Sweet Potato Layer
- 1.5 lbs sweet potatoes (about 2-3 sweet potatoes, sliced thinly on a mandoline, ⅛” thickness)
Sauce
- 3 Tablespoons butter
- ½ cup onion (finely chopped)
- 3-4 garlic cloves (finely minced)
- 1 cup heavy whipping cream
- 1 Tablespoon arrowroot starch (or cornstarch)
- Juice of ½ lemon
Seasoning and Cheese
- 1 cup Parmesan cheese (thinly grated, divided)
- Salt and pepper (to taste)
- 1 teaspoon rosemary
Instructions
- Preheat and Prepare Dish: Preheat your oven to 400°F (205°C). Grease the sides of a baking dish thoroughly with butter or olive oil to prevent sticking.
- Sauté Onion and Garlic: Melt butter in a small skillet over medium-high heat. Add finely chopped onion and sauté until translucent and tender, about 2-3 minutes. Add minced garlic and cook for another 30 seconds until fragrant, careful not to burn.
- Make Cream Sauce: Pour in the heavy whipping cream and stir to combine. In a small bowl, mix the arrowroot starch with a little of the warm cream to create a slurry. Add the slurry back into the skillet with the cream and stir continuously until the sauce thickens. Remove from heat and set aside.
- Layer Sweet Potatoes: Arrange a single layer of thinly sliced sweet potatoes overlapping in the greased baking dish. Season this layer with salt, pepper, and rosemary. Pour half of the prepared onion-cream mixture over the sweet potatoes and sprinkle with half of the Parmesan cheese.
- Second Layer: Add another overlapping layer of sweet potato slices. Again, season with salt, pepper, and rosemary. Pour the remaining onion-cream sauce on top and finish with the remaining Parmesan cheese.
- Bake: Place the baking dish in the preheated oven and bake uncovered for 30-40 minutes, or until the sweet potatoes are tender and the top is lightly golden. The sauce should be bubbling and thickened.
- Rest and Serve: Remove from oven and let the gratin rest for 5-10 minutes. This allows the sauce to thicken up further. Serve warm as a delicious side dish to your meal.
Notes
- Using a mandoline slicer ensures uniformly thin slices, which helps the gratin cook evenly.
- The arrowroot starch can be substituted with cornstarch if unavailable.
- Letting the gratin rest before serving improves sauce consistency.
- Fresh rosemary adds a fragrant herbal note, but you may substitute with thyme if preferred.
- For a richer flavor, try mixing Parmesan with Gruyère cheese.
- To lighten the dish, you can use half-and-half instead of heavy cream, but the sauce may be less thick.
- Prep Time: 15 minutes
- Cook Time: 35 minutes
- Category: Side Dish
- Method: Baking
- Cuisine: American
