Sweet Potatoes Au Gratin With Sharp Cheddar
Thinly sliced sweet potatoes layered with garlicky cream and sharp cheddar, baked until the top browns. The savory answer to the marshmallow casserole.
Servings 6 servings
Ingredients
For the Gratin
- 2 ½ lbs sweet potatoes peeled and sliced ⅛ inch thick
- 1 ½ cups heavy cream
- 3 cloves garlic minced
- 1 tablespoon fresh thyme leaves chopped
- ⅛ teaspoon freshly grated nutmeg
- 1 ½ teaspoons kosher salt
- ¾ teaspoon black pepper
- 8 oz sharp cheddar grated from a block, about 2 cups
- ½ cup Parmesan finely grated
- 1 tablespoon unsalted butter for the dish
Instructions
Prep
- Heat the oven to 375F and butter a 9x13 inch baking dish.
- Peel the sweet potatoes and slice them ⅛ inch thick, ideally on a mandoline. Do not soak the slices in water.
- Grate the cheddar from a block and finely grate the Parmesan. Keep them in separate bowls.
Infuse the Cream
- Combine the cream, garlic, thyme, nutmeg, salt, and pepper in a small saucepan over medium-low heat.
- Bring it just to the edge of a simmer, about 4 minutes, then take it off the heat.
Layer and Bake
- Shingle a third of the sweet potato slices across the bottom of the dish, overlapping them. Scatter a third of the cheddar over the top with a small pinch of salt and pepper.
- Repeat twice more, finishing with a layer of cheddar.
- Pour the warm cream evenly over the surface, then press the whole stack down firmly with your palms so the cream reaches the bottom layer.
- Cover tightly with foil and bake for 40 minutes.
- Remove the foil, scatter the Parmesan over the top, and bake uncovered for another 20 to 25 minutes, until browned in patches and bubbling at the edges.
- Rest on the counter for 15 minutes before serving so the cream sets.
Notes
- Grate your own cheese: bagged shredded cheddar is coated in starch and turns grainy in cream. Use a block.
- Heavy cream only: milk and half and half carry less fat and are much more likely to curdle over a long bake.
- Even slices matter more than thin slices: mixed thicknesses cook at different rates and you lose the texture.
- Make ahead: assemble up to 24 hours in advance, refrigerate covered, and add 10 to 15 minutes to the covered bake.
- Leftovers: crisp cold squares in a buttered skillet and top with a fried egg.