This savory sweet potato gratin is what happens when a French gratin meets a Greek kitchen. Thin rounds of sweet potato are layered with nutty Graviera (or Gruyère), little cubes of prosciutto, and a silky custard of cream infused with sage, thyme, cloves, and nutmeg. It bakes up golden and bubbling, creamy in the middle and crisp at the edges — sweet, salty, and herby all at once.

In our house, this gratin is a delicious compromise. Daryl grew up on marshmallow-topped sweet potatoes and would happily have them every holiday. But I’m Greek, and I just can’t put marshmallows on a savory dish. This gratin is where we meet in the middle: he gets his sweet potatoes, I get my cheese and herbs, and we both go back for seconds. It holds its own next to a roast chicken on a Sunday, and it’s easy to assemble ahead when you’re cooking for a crowd.

Love sweet potatoes in savory dishes? Try my sweet potato moussaka and roasted cinnamon chicken with sweet potatoes.

Savory sweet potato gratin with Graviera and prosciutto

Overview

Why you will love sweet potato gratin

Sweet meets savory – Caramelized sweet potatoes, nutty Graviera, and salty prosciutto balance each other. Comforting, but not cloying.
A spiced custard, not a flour sauce – Most sweet potato au gratin recipes start with a roux. Here the cream simmers with garlic, sage, thyme, cloves, and nutmeg, then gets whisked into eggs, so the layers set into slices that hold their shape.
Make-ahead friendly – Assemble it a few hours early and bake when you need it, or bake it fully and reheat.
A crowd-pleaser – It’s the savory sweet potato casserole for people who don’t like sweet potato casserole.
Goes with everything – Roast chicken, pork, turkey, lamb, or a big green salad for a meatless dinner.

Close-up of sweet potato au gratin topped with crispy prosciutto and fresh sage

Ingredients for sweet potato gratin

Sweet potatoes – Use any variety you like. Mixing red and purple sweet potatoes creates a gorgeous, colorful dish that looks stunning on the table.
Graviera cheese (or Gruyère) – Graviera is Greece’s answer to Gruyère: nutty, a little sweet, and a beautiful melter. The best-known comes from Crete and is made mostly from sheep’s milk, which gives it a richer, slightly tangy edge. Look for it at Greek or Mediterranean markets; Gruyère is a perfect stand-in.
Prosciutto cubetti – These small, thick cubes of prosciutto are perfect for this gratin and save you the trouble of cutting thin slices. They’re easy to find in most supermarkets. You can also substitute with pancetta or bacon for a similar savory kick.
Butter – I prefer salted butter for extra flavor, but you can use your favorite.
Heavy cream – Rich and luscious, it binds the layers together. For a lighter version, substitute half-and-half or whole milk.
Eggs – Fresh, organic, and free-range if possible, always worth it for flavor and texture.
Fresh sage and thyme – They infuse the cream and get strained out, so use whole leaves and sprigs. Save a few small sage leaves to scatter on top before serving if you like. Dried herbs work in a pinch — strain the cream through a fine sieve. In Greece, sage is faskomilo (φασκόμηλο). Greek sage grows wild on the hillsides, and we brew it as a tea as often as we cook with it. (Don’t confuse it with Greek mountain tea, tsai tou vounou, which is a different herb.)
Cloves and ground nutmeg – These warming spices add a subtle sweetness that makes the cream mixture smell like Christmas custard.
Garlic – Just a touch adds depth and rounds out the flavors.
Sea salt and freshly ground pepper – Essential for balancing the sweetness of the potatoes and the richness of the cheese.

How to make this sweet potato au gratin

Heavy cream simmering with sage, thyme, cloves, garlic and nutmeg

Preheat the oven to 400°F (200°C). In a medium pot, combine the cream, a few sage leaves, cloves, thyme sprigs, minced garlic, ground nutmeg, and a pinch of sea salt. Bring to a gentle simmer and cook for about 10 minutes, until slightly reduced and fragrant. Strain the mixture through a fine sieve to remove the herbs and cloves.

Whisking warm infused cream into beaten eggs to make the gratin custard

In a large bowl, lightly whisk the eggs. Slowly pour in the warm cream while whisking constantly so the eggs don’t scramble. Mix well and set aside.

Layering sweet potato gratin: buttered dish, sweet potato slices, custard, Graviera and prosciutto

Generously butter your baking dish (approximately 10.5″ x 7.5″). Sprinkle a little grated Graviera over the bottom to create a flavorful base. (image 1)
Layer the sweet potatoes: Arrange a layer of sweet potato slices, slightly overlapping. Season with a pinch of salt and pepper. Pour over ⅓ of the cream-egg mixture, then sprinkle with ⅓ cup Graviera and ¼ cup prosciutto cubetti. (image 2)
Repeat the layering process, adding potatoes, seasoning, cream mixture, cheese, and prosciutto two more times, ending with the final layer of potatoes, the remaining cream mixture, and toppings. (images 3-4)
Cover the dish with a buttered sheet of foil and bake for about 40 minutes, until the potatoes are tender when pierced with a knife.

Sweet potato gratin after the covered bake, ready for the final layer of cheese

Remove the foil, sprinkle the top with the remaining Graviera, and bake uncovered for another 25–30 minutes, until golden brown and bubbling, a knife slides through the center with no resistance, and the center reaches 160°F (71°C) on an instant-read thermometer (the custard has eggs). Let it rest 10–15 minutes before serving.

Tips for the best sweet potato gratin

Slice evenly: Use a mandoline or sharp knife to slice the sweet potatoes uniformly, this ensures they cook evenly and layer beautifully.
Warm the cream gently: Don’t let it boil too hard; gentle simmering helps infuse the herbs and keeps the cream silky.
Gruyère vs. Graviera: If you can find Greek Graviera, try it! It adds a distinct nutty flavor and a touch of Greek authenticity.
Make ahead: Assemble the gratin a few hours before baking. Cover and refrigerate, then bake just before serving.
For a crispier top: Broil for 2–3 minutes at the end, but keep an eye on it so it doesn’t burn.
Let it rest: Give it 10–15 minutes after baking. This allows the custard to set and makes serving easier.

Baked sweet potato gratin with golden, bubbling Graviera and two serving spoons

Serving suggestions

This sweet potato gratin makes a wonderful side dish for both everyday dinners and festive occasions. It’s rich, aromatic, and pairs beautifully with roasted meats and fresh salads.

Holiday mains: Serve alongside roast herb butter turkey, pork pot roast, or roasted leg of lamb for a show-stopping holiday table.
Simple pairings: It also pairs well with grilled chicken skewers, baked salmon, or a crispy green salad with lemon vinaigrette for a lighter meal.
Vegetarian spread: Skip the prosciutto for a meat-free version and pair it with roasted vegetables or a hearty lentil salad.
Make it part of a Greek-style feast: Add maroulosalata, Greek lemon potatoes, and a savory cheese pie (tiropita) to create a full Mediterranean menu.

Storage and reheating

Refrigerate: Store leftovers in an airtight container in the refrigerator for up to 3 days.
Reheat: Warm individual portions in the microwave or reheat the whole dish in a 350°F (175°C) oven, covered with foil, until heated through (about 20 minutes).
Avoid drying out: Add a splash of milk or cream before reheating to restore the creamy texture.
Not ideal for freezing: The custard and cheese can separate once thawed, so this gratin is best made fresh or enjoyed within a few days.

Sweet potato gratin FAQs

Yes! You can assemble the gratin a few hours before baking, cover it tightly with foil, and refrigerate. When ready to serve, bake as directed. If baking straight from the fridge, add about 10 extra minutes to the cooking time.

Absolutely. Simply omit the prosciutto or replace it with sautéed mushrooms, caramelized onions, or sun-dried tomatoes for extra depth of flavor.

If Graviera or Gruyère isn’t available, try Emmental, Comté, or sharp white cheddar.

It’s up to you! The peel adds texture and nutrients. For a smoother gratin, peel them first. For a rustic look, leave the skins on.

A sweet potato casserole is usually mashed sweet potatoes sweetened with brown sugar and topped with marshmallows or pecans. A sweet potato gratin (or sweet potatoes au gratin) is sliced sweet potatoes baked in layers with cream and cheese until golden on top — savory rather than sweet.

Both are thinly sliced and baked in cream. “Au gratin” means there’s cheese (and often a crisp, browned top); scalloped versions traditionally skip the cheese.