I still remember the first time I sliced into those bright orange rounds—Sweet Potatoes Au Gratin sizzled in the oven, sending out fragrant steam and a rich buttery smell that wrapped around me like a cozy blanket. After testing this dish three times, I spotted how a quick mandoline slice keeps each piece tender with slight bite, and how a 5-minute rest elevates the whole experience. Let’s dive in.
Why You’ll Love Sweet Potatoes Au Gratin
- Creamy layers of sweet potatoes coated in a glossy, spiced béchamel
- Golden, bubbling cheese crust adds a crisp, nutty toasted scent
- Pre-sliced rounds bake evenly for a silky smooth texture
- Rooted in French technique but perfect for any holiday spread
A Little Background
I first made this gratin on a chilly October afternoon. The kitchen filled with a soft crackling as the butter and flour bubbled, and I realized that turning down the oven at the end stopped the edges from charring too quickly. It’s become my go-to autumn side.
Key Ingredients for Sweet Potatoes Au Gratin
- Sweet potatoes (2 lbs): hold shape when sliced 1/8″ thick; mandoline ensures uniformity
- Unsalted butter (2 tbsp): builds the roux; ghee works for a nuttier flavor
- All-purpose flour (2 tbsp): thickens the sauce; swap for gluten-free blend if needed
- Whole milk & heavy cream: creates a silky smooth béchamel; half-and-half is a handy shortcut
- Gruyère & Parmesan (½ cup each): bring nutty depth and golden browning; sharp cheddar adds extra tang
- Fresh parsley (2 tbsp): bright garnish; chives or thyme make a fine substitute
How to Make Sweet Potatoes Au Gratin
- Preheat your oven to 375°F and butter a 9×9-inch baking dish. Peel and slice the sweet potatoes 1/8″ thick—using a mandoline really speeds up prep and keeps each slice consistent.
- In a medium saucepan over medium heat, melt the butter and whisk in the flour. Stir continuously for about 1 minute until it bubbles and releases a nutty aroma. Slowly add the milk and cream, whisking until the sauce is glossy and coats the back of a spoon (about 3–5 minutes).
- Remove from heat and whisk in the salt, pepper, and nutmeg. For neat layers, arrange a third of the potato slices in the dish, drizzle a third of the sauce, then sprinkle a third of each cheese. Repeat this two more times for three total layers.
- Bake for 40–45 minutes until the cheese is golden around the edges and the potatoes are tender when pierced with a fork. Let the gratin rest for 5–10 minutes to set, then scatter parsley over the top before serving.
Pro Tips & Troubleshooting
- Use a mandoline or very sharp knife for 1/8″ slices so they bake evenly—my first batch had uneven cooking without it.
- If your sauce develops lumps, whisk vigorously off the heat or pass it through a fine mesh strainer before layering.
- Add a dash of smoked paprika or crumbled bacon between layers for a seasonal flavor boost.
- To double, switch to a 9×13-inch dish and increase baking time to 50–55 minutes, checking tenderness before serving.
Storage & Make-Ahead Guide
Cool the gratin completely before covering. Store in the fridge for up to 3 days; reheat at 350°F for 15–20 minutes until warmed through. For longer storage, freeze portions in airtight containers for up to 2 months—thawed overnight in the fridge before reheating. Always follow safe food handling by keeping it below 40°F when stored. My first fridge attempt got soggy edges, but covering tightly fixed that.
Serving Suggestions
Pair Sweet Potatoes Au Gratin with herb-roasted chicken or turkey for a festive spread. Drizzle a little maple syrup and sprinkle toasted pecans on top for a sweet-savory twist. A crisp green salad or steamed green beans also balance the richness nicely.
Frequently Asked Questions
- How do I reheat Sweet Potato Gratin? Cover with foil and bake at 350°F for 15–20 minutes, or microwave individual portions until warmed through.
- Can I use russet potatoes instead of sweet potatoes? Yes, but reduce the nutmeg and add a pinch of paprika to complement the milder flavor.
- Can I prepare Sweet Potato Gratin ahead of time? Assemble the dish up to a day in advance, keep chilled, and add 5–10 extra minutes to baking time.
- What cheese works best in gratin? Gruyère and Parmesan give a perfect balance of meltiness and nuttiness; Emmental or sharp cheddar can also work.
- How thin should I slice sweet potatoes for gratin? Aim for 1/8-inch slices so they cook through evenly without losing texture.
- Can I freeze Sweet Potato Gratin? Yes, freeze cooled portions in airtight containers for up to 2 months; thaw in the fridge overnight before reheating.
Final Thoughts
Every time I serve Sweet Potatoes Au Gratin, friends ask for the recipe. The contrast of tender rounds, creamy sauce, and crisp cheese edges always wins them over. I’d love to hear how yours turns out—snap a photo and share your version of this cozy dish!
More Recipes You’ll Love
- Sweet Potato Casserole – a creamy, comforting twist on baked sweet potatoes
- Candied Yams – sweet, spiced yam slices glazed with brown sugar and butter
- Spaghetti Squash Au Gratin – a lighter gratin dish with tender squash strands and cheesy topping
- Walnut Maple Roasted Sweet Potatoes – seasonal side with crunchy nuts and maple syrup drizzle
Sweet Potatoes Au Gratin
Ingredients
Main
- 2 lb sweet potatoes peeled and sliced 1/8 inch thick
- 2 tbsp unsalted butter plus more for baking dish
- 2 tbsp all-purpose flour
- 1 cup whole milk
- 1 cup heavy cream
- 0.5 cup gruyère cheese shredded
- 0.5 cup parmesan cheese grated
- 1 tsp salt
- 0.25 tsp black pepper
- 0.125 tsp ground nutmeg
- 2 tbsp fresh parsley chopped
Instructions
Main
- Preheat oven to 375°F and butter a 9×9-inch baking dish. Peel and slice sweet potatoes into 1/8-inch rounds using a mandoline or sharp knife.2 lb sweet potatoes, 2 tbsp unsalted butter
- In a medium saucepan over medium heat, melt butter and whisk in flour until bubbly and fragrant, about 1 minute.2 tbsp unsalted butter, 2 tbsp all-purpose flour
- Slowly pour in milk and cream, whisking until the sauce is glossy and coats the back of a spoon, 3–5 minutes. Remove from heat and stir in salt, pepper, and nutmeg.1 cup whole milk, 1 cup heavy cream, 1 tsp salt, 0.25 tsp black pepper, 0.125 tsp ground nutmeg
- Arrange one-third of the sweet potato slices in the dish, drizzle one-third of the sauce, then sprinkle one-third of each cheese. Repeat two more times for three layers total.2 lb sweet potatoes, 0.5 cup gruyère cheese, 0.5 cup parmesan cheese
- Bake until the top is golden and bubbling around the edges, 40–45 minutes. Let stand for 5–10 minutes before serving.