Equipment
Ingredients
Gratin Ingredients
- 1000 g sweet potato, peeled and sliced into 3mm uniform rounds
- 350 ml heavy cream, liquid
- 180 g gruyere cheese, freshly shredded
- 4 garlic, peeled and finely minced
- 6 g fine sea salt, dry ground
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 473 kcal
- Protein
- 13 g
- Carbohydrates
- 36 g
- Fat
- 31 g
- Fiber
- 5 g
- Sugar
- 9 g
- Sodium
- 710 mg
- Saturated Fat
- 19 g
- Monounsaturated Fat
- 8 g
- Polyunsaturated Fat
- 1 g
- Cholesterol
- 100 mg
- Potassium
- 655 mg
- Calcium
- 398 mg
- Iron
- 1.2 mg
- Magnesium
- 57 mg
- Phosphorus
- 299 mg
- Zinc
- 1.9 mg
- Vitamin A
- 1505 mcg
- Vitamin C
- 5 mg
- Vitamin D
- 1.1 mcg
- Vitamin E
- 1.1 mg
- Vitamin K
- 6 mcg
- Vitamin B6
- 0.4 mg
- Vitamin B12
- 0.6 mcg
- Thiamin
- 0.17 mg
- Riboflavin
- 0.30 mg
- Niacin
- 1.0 mg
- Folate
- 24 mcg
- Water
- 175 g
- Alcohol
- 0 g
- Caffeine
- 0 mg
Sources: USDA FoodData Central
Method
Preheat the oven to 190°C (375°F) with a rack set in the middle position.
Using a mandoline slicer set on a cutting board, slice the peeled sweet potatoes into uniform 3mm rounds.
Combine the heavy cream, minced garlic, and fine sea salt in a small saucepan over medium-low heat, warming until steam rises gently but the mixture does not simmer.
Arrange one-third of the sweet potato slices across the bottom of the 2-quart ceramic baking dish in neat, overlapping rows.
Pour one-third of the warm garlic cream evenly over the arranged sweet potatoes and scatter one-third of the shredded Gruyere cheese over the surface.
Repeat the layering sequence two more times with the remaining sweet potatoes, cream, and shredded Gruyere cheese to form three full tiers ending with cheese on top.
Cover the 2-quart ceramic baking dish tightly with aluminum foil and bake at 190°C (375°F) for 45 minutes until the sweet potatoes are tender when pierced with a paring knife.
Remove the aluminum foil and continue baking uncovered at 190°C (375°F) for 15 minutes until the top cheese crust is bubbling and deep golden brown.
Transfer the dish to a heatproof surface and rest at room temperature for 15 minutes before portioning and serving.
Chef's Notes
- Sweet potatoes release less free starch than Russet potatoes, so full-fat heavy cream is necessary to provide viscosity and body without graininess.
- Do not rinse or soak sliced sweet potatoes in water; retaining their surface starches helps bind the cream and cheese into a cohesive gratin.
- Using freshly grated cave-aged Gruyere from a block provides significantly better melting performance and deeper nuttiness than pre-shredded cheese containing anti-caking starches.
- For clean presentation slices on a festive table, bake the gratin several hours ahead, chill until firm, slice into neat portions, and reheat covered to 74°C (165°F).
Storage
Refrigerator: 4 days — Cool within 2 hours of baking and store in an airtight container or covered tightly in the baking dish.
Freezer: 2 months — Wrap chilled portions tightly in plastic wrap and aluminum foil; thaw in refrigerator for 24 hours before reheating.
Reheating: Reheat refrigerated leftovers in an oven preheated to 175°C (350°F) for 20 to 25 minutes or in a microwave until the internal temperature reaches at least 74°C (165°F) throughout before serving.
Troubleshooting
The cream sauce splits, appearing greasy and grainy rather than silky
Cause: The oven ran too hot or lower-fat dairy was substituted, causing the milk emulsion to break under extreme heat
Fix: Cannot be fixed once fully baked, but resting the gratin 15 to 20 minutes allows the starches to reabsorb free lipids
Prevention: Use heavy cream with at least 36 percent milk fat and verify oven accuracy with an internal thermometer
Sweet potatoes in the center remain firm while edges are soft
Cause: Sweet potato slices were cut too thickly or the dish was not sealed tightly with foil during the steam phase
Fix: Cover the dish with foil again and return to the oven at 190°C (375°F) for 10 to 15 additional minutes until knife-tender
Prevention: Slice rounds precisely to 3mm and crimp foil firmly around the baking dish rim to trap moisture
The cheese crust darkens excessively before potatoes are cooked through
Cause: The foil was removed prematurely or the dish was positioned too close to the top heating element
Fix: Tent loosely with a fresh sheet of aluminum foil to shield the crust from direct heat while finishing the bake
Prevention: Bake covered for the full 45 minutes on the center rack before uncovering
Cultural Context
Rooted in the classic French gratin dauphinois tradition of southeastern France, this adaptation replaces starchy white potatoes with sweet potatoes. The assertive nuttiness of Alpine Gruyere and the pungency of garlic temper the sweet tuber, making it an enduring staple on contemporary winter and Christmas holiday menus.
