Enjoy sweet potatoes in a new, irresistible way with these Sweet Potato Au Gratin. Thin rounds of sweet potato are layered in a rich, cheesy cream sauce and finished with a crispy crumb topping made from Ritz crackers for a buttery, crunchy crust. The result is a comforting, elegant side dish that works equally well for weeknight dinners or special holiday meals.
If you love traditional sweet potato casserole, try swapping to au gratin for a creamier, cheesier experience. The potato rounds stay tender while the cheese sauce binds the layers together, and the cracker crumbs create a satisfying contrast in texture. This recipe is straightforward: slice the potatoes thin, prepare the au gratin sauce, assemble the layers in a 9×13-inch casserole dish, top with crumbs and bake until bubbling and golden.
What You Need for Sweet Potato Au Gratin
- 9×13-inch casserole dish: the correct size helps the dish cook evenly and fit the layers well.
- Mandoline or sharp knife: thin, uniform slices are key — aim for about 1.3mm to 2mm thickness for even cooking.
- Sweet potatoes: any variety will work; mixing colors adds visual appeal.
A mandoline makes it quick and easy to get very thin, even slices, but a steady hand with a sharp knife can do the job if you prefer. Thin slices ensure a creamy interior and a nicely browned edge where the sauce caramelizes slightly.
Variations and Substitutions
- Potato choice: If you prefer, use regular potatoes such as Yukon gold for a more classic potato au gratin.
- Herbs: Fresh thyme works beautifully, but you can swap in sage, rosemary, parsley, or oregano to change the flavor profile.
- Milk: Use a fuller-fat dairy milk for a richer sauce, or a plant-based milk if you need a dairy-free option (note texture may vary).
- Cheese: Parmesan and gruyere are classic here, but shredded cheddar, havarti, or gouda will also melt nicely and add great flavor.
FAQ
What is the difference between scalloped and gratin potatoes?
Scalloped potatoes are typically made with a cream sauce but do not include cheese, while gratin potatoes add cheese between the layers and on top. That addition of cheese changes both flavor and texture, making gratin richer and more savory.
Why are my au gratin potatoes watery?
Excess moisture most often comes from not drying the sliced potatoes well after rinsing or soaking. Pat the slices dry before assembling so the sauce stays thick and creamy rather than watery.
Can I make au gratin sweet potatoes ahead of time?
Yes. You can slice the potatoes and store them submerged in ice-cold water in the refrigerator for several hours or overnight. Assemble the dish when ready to bake; this saves time when preparing for guests.
Storage + Freezer Directions
Store any leftovers in an airtight container in the refrigerator for up to 5 days. Reheat gently in the oven until warmed through to preserve texture.
Can you freeze sweet potato au gratin?
To freeze: Cover the baked dish tightly with aluminum foil or plastic wrap, or transfer cooled portions to a freezer-safe, airtight container. Freeze for up to 2 months. Thaw overnight in the refrigerator before reheating in the oven.
How to Serve Sweet Potato Au Gratin
These au gratin sweet potatoes pair well with roasted or braised proteins and other hearty fall sides. Serve alongside roasted pork loin, pan-seared chicken breast, smoked turkey legs, or a variety of seasonal vegetables like balsamic-grilled Brussels sprouts, roasted root vegetables, or a fresh apple burrata salad for balance.
Sweet Potato Au Gratin recipe
These au gratin sweet potatoes are cheesy, creamy, and a delicious twist on classic au gratin. They make a standout side for holidays and weeknight dinners alike.
By: Linley Hanson
Prep: 30 mins • Cook: 1 hr • Total: 1 hr 30 mins • Servings: 10
Ingredients
- 3 large sweet potatoes, any color
Au Gratin Sauce
- 6 tablespoons unsalted butter
- ½ medium yellow onion, minced
- ½ teaspoon sea salt, divided
- 6 cloves garlic, minced
- ⅓ cup all-purpose flour
- ½ teaspoon cracked black pepper
- 1 tablespoon chopped fresh thyme
- 1½ cups 2% milk (or preferred milk)
- 1 cup chicken broth
- 1 cup grated Parmesan cheese
- 1 cup shredded Gruyere cheese
Topping
- 15 Ritz crackers, crumbled (or gluten-free breadcrumbs)
- 2 tablespoons fresh thyme, chopped
Instructions
- Preheat the oven to 400°F (200°C) and grease a 9×13-inch casserole dish.
- Slice the sweet potatoes into uniform rounds using a mandoline or a very sharp knife. Aim for about 1.3mm–2mm thickness. Avoid slices that are too thick so they cook evenly.
- To make the sauce, melt the butter in a large skillet over medium-high heat. Add the minced onion and ¼ teaspoon of the salt; sauté 3–4 minutes until softened. Add the garlic and sauté another minute until fragrant.
- Stir in the flour, cracked black pepper, and chopped thyme to form a paste; cook 1 minute to eliminate the raw flour taste.
- Reduce heat to medium and slowly whisk in the milk, stirring constantly to prevent scorching. The mixture will thicken as it heats.
- Add the chicken broth gradually while whisking until the sauce is smooth and thickened.
- Remove from heat and whisk in the Parmesan and Gruyere a little at a time until fully melted and the sauce is smooth (it will still contain the softened onion and garlic).
- Pour about 1 cup of the cheese sauce into the bottom of the prepared dish and spread it evenly. Arrange a single layer of sweet potato rounds (skin side up) to cover the dish.
- Pour the remaining sauce over the potatoes, using a spatula to work it down between the slices so each layer is coated.
- Sprinkle the crumbled Ritz crackers evenly over the top and cover the casserole dish with foil.
- Bake covered for 30 minutes, then remove the foil and bake an additional 30 minutes uncovered, until potatoes are tender and the top is golden and crisp.
- Remove from the oven and let rest for 10 minutes before serving. Garnish with the remaining fresh thyme.
Tips & Notes
- Gluten-free breadcrumbs can replace the Ritz crackers if needed.
- Keep the casserole uncovered for the second half of baking so excess liquid evaporates and the sauce thickens.
- Let the dish rest after baking to allow the sauce to set slightly; this makes serving cleaner slices easier.
Nutrition
Calories: 279 kcal • Carbohydrates: 24 g • Protein: 10 g • Fat: 16 g • Fiber: 3 g • Sugar: 5 g
Nutrition information is automatically calculated and should be used as an approximation.
Photography: photos in this post were taken by Ashley McGlaughlin from The Edible Perspective.