Equipment
* optional
Ingredients
Produce
- 700 g sweet potato, whole, unpeeled
- 400 g apple, whole, firm tart-sweet variety like Honeycrisp or Granny Smith
- 400 g pear, whole, firm variety like Bosc or Anjou
- 2 orange, fresh, whole
Glaze and Seasonings
- 120 ml vegetable broth, low-sodium, room temperature
- 30 ml maple syrup, pure grade A dark
- 30 ml toasted walnut oil, pure, cold-pressed, divided use (20ml in glaze, 10ml for finishing)
- 5 g fresh thyme leaves, stemmed and finely chopped
- 5 g fine sea salt, dry
- 1 g ground black pepper, freshly ground
- ½ g ground nutmeg, freshly grated
- 10 ml olive oil, liquid, for coating baking dish
Topping
- 50 g raw walnuts, coarsely chopped
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 273 kcal
- Protein
- 3 g
- Carbohydrates
- 43 g
- Fat
- 12 g
- Zinc
- 0.8 mg
Sources: Aggregated Public Data, USDA FoodData Central
Method
Preheat the oven to 190°C (375°F) with an oven rack set in the center position.
Coat the bottom and sides of the baking dish (28x18 cm / 2-quart) evenly with 10 ml olive oil using a pastry brush.
Peel the sweet potatoes, apples, and pears on a cutting board using a vegetable peeler, trimming and discarding the stem and root ends.
Cut the sweet potatoes, apples, and pears into uniform 3 mm thick rounds using a mandoline slicer, coring the apple and pear slices with a small chef knife to remove inner seeds.
Grate the outer zest from the oranges into a small mixing bowl using a zester or microplane, then halve the oranges and extract 120 ml of fresh juice using a juicer.
Add the 120 ml fresh orange juice, vegetable broth, maple syrup, 20 ml of the toasted walnut oil, fresh thyme leaves, fine sea salt, ground black pepper, and ground nutmeg to the bowl, then blend thoroughly using a whisk.
Arrange the sliced sweet potatoes, apples, and pears in the prepared baking dish in tight, alternating rows, shingling the slices at a slight upward angle.
Pour the whisked orange and walnut oil liquid evenly over the shingled layers in the baking dish, ensuring all exposed edges are moistened.
Cover the baking dish tightly with aluminum foil and bake in the preheated oven at 190°C (375°F) for 40 minutes until the sweet potatoes yield easily when pierced with the tip of a chef knife.
Remove the aluminum foil, scatter the 50 g of chopped raw walnuts evenly across the top, and drizzle with the remaining 10 ml of toasted walnut oil.
Return the uncovered dish to the oven at 190°C (375°F) and bake for 20 minutes until the liquid reduces to a glossy syrup, the walnuts become golden, and the exposed fruit edges caramelize.
Rest the baking dish on a heatproof surface at room temperature for 10 minutes to allow the reduced citrus glaze to thicken before serving.
Chef's Notes
- Select firm, dense varieties of fruit like Bosc pears and Honeycrisp or Granny Smith apples so the layers retain structural definition rather than disintegrating during braising.
- Dividing the walnut oil preserves its delicate aromatics: the portion whisked into the glaze infuses the layers with deep warmth, while the finishing drizzle delivers a fresh roasted fragrance.
- Arranging slices at a slight 45-degree angle rather than flat creates the classic gratin contrast: tender, broth-braised bases and crispy, concentrated caramelized tips.
- A clean mandoline cut is vital; irregular, hand-cut wedges will lead to unevenly cooked bites where sweet potato remains starchy while pear dissolves.
Storage
Refrigerator: 4 days — Cool completely and store in an airtight container at or below 4°C (40°F) within 2 hours of baking.
Freezer: 2 months — Freeze in a sealed airtight container. Thaw overnight in the refrigerator before reheating; note fruit will be slightly softer.
Reheating: Reheat refrigerated leftovers in an oven preheated to 175°C (350°F) covered with foil until the internal temperature reaches at least 74°C (165°F), approximately 15 to 20 minutes.
Troubleshooting
Sweet potatoes are firm and undercooked while apples and pears have turned mushy
Cause: Sweet potatoes were sliced significantly thicker than the fruit or the dish was not sealed tightly with foil during the initial bake
Fix: Cover the dish with foil again, add 30 ml hot vegetable broth, and bake at 190°C (375°F) for an extra 10 to 15 minutes
Prevention: Slice all produce uniformly to 3 mm on a mandoline and crimp foil securely around the dish edges to trap steam
Walnut topping burns before the gratin edges are caramelized
Cause: Walnuts were added at the start of baking or the oven rack was positioned too close to the upper heating element
Fix: Carefully pick off the scorched nuts and replace with freshly toasted chopped walnuts before bringing the dish to the table
Prevention: Add walnuts only for the final 20 minutes of uncovered baking and keep the dish centered in the oven
The braising sauce remains thin and watery after baking
Cause: The fruit released higher than average water content or the uncovered baking phase was cut short
Fix: Tilt the baking dish and spoon excess liquid into a small saucepan, boil over medium-high heat for 3 to 4 minutes to reduce to a glaze, then pour back over the gratin
Prevention: Choose firm, low-moisture baking varieties such as Bosc pears and Honeycrisp apples
Cultural Context
Originating in the French Dauphine region, classic gratins feature thin root vegetables slow-baked in rich dairy until browned and crusty. This seasonal American adaptation translates the technique to the Thanksgiving and autumn harvest table, replacing heavy cream with bright citrus juice, rich walnut oil, and orchard fruits to create an elegant, plant-based centerpiece.
