Equipment
* optional
Ingredients
Vegetables and Aromatics
- 800 g yukon gold potatoes, peeled and sliced to 3 mm thickness
- 220 g swiss chard stems, washed, trimmed, and sliced into 5 mm pieces
- 3 garlic, finely grated
- 3 g fresh thyme leaves, finely chopped
Dairy and Seasoning
- 350 ml heavy cream
- 150 ml whole milk
- 150 g gruyère cheese, freshly shredded
- 20 g unsalted butter, softened
- 8 g fine sea salt
- 1½ g black pepper, freshly cracked
- ½ g ground nutmeg, freshly grated
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 450 kcal
- Protein
- 13 g
- Carbohydrates
- 27 g
- Fat
- 33 g
- Zinc
- 1.9 mg
- Water
- 209 g
Sources: Aggregated Public Data, USDA FoodData Central
Method
Preheat the oven to 190°C (375°F) with a rack arranged in the middle position.
Grease the bottom and sides of a 2-quart ceramic baking dish thoroughly using 10 g of softened unsalted butter.
Slice the trimmed Swiss chard stems crosswise into uniform 5 mm slices using a chef knife and cutting board.
Slice the peeled Yukon Gold potatoes into uniform 3 mm thick rounds using a mandoline slicer, keeping them unrinsed to retain natural surface starches.
Combine 350 ml heavy cream, 150 ml whole milk, 3 finely grated garlic cloves, 8 g fine sea salt, 1.5 g cracked black pepper, 0.5 g ground nutmeg, and 3 g chopped fresh thyme leaves in a medium saucepan.
Simmer the cream mixture over medium-low heat for 4 minutes until warm, aromatic, and steaming gently, ensuring it does not reach a rapid boil.
Arrange half of the sliced potatoes in neat, slightly overlapping rows across the base of the buttered ceramic baking dish.
Scatter all 220 g of the sliced Swiss chard stems in an even layer directly over the bottom layer of potatoes.
Sprinkle 75 g of the shredded Gruyère cheese uniformly over the layer of Swiss chard stems.
Arrange the remaining sliced potatoes in overlapping rows over the cheese and chard layer to form a smooth top surface.
Pour the warm seasoned cream mixture slowly and evenly over the layered dish, pressing down lightly with the back of a spoon to submerge the ingredients.
Scatter the remaining 75 g of shredded Gruyère cheese over the top surface and dot evenly with the remaining 10 g of diced butter.
Cover the baking dish tightly with aluminum foil and bake at 190°C (375°F) for 40 minutes.
Remove the aluminum foil and bake uncovered at 190°C (375°F) for 20 minutes until the top is deeply golden brown and the cream is bubbling vigorously around the edges.
Rest the gratin undisturbed on a wire rack at room temperature for 15 minutes before portioning and serving.
Chef's Notes
- Retaining natural surface starches on the potato slices is paramount; do not rinse or soak them after slicing, as this starch binds the dairy into a velvet sauce without flour.
- Swiss chard stems contain dense plant fiber and moisture; slicing them thinly to 5 mm ensures they soften synchronously with the 3 mm potato slices during the braising stage.
- A ratio of 70 percent heavy cream to 30 percent whole milk yields ideal mouthfeel, providing sufficient butterfat to resist curdling from natural vegetable acidity without becoming greasy.
- Gruyère provides savory depth and reliable melting qualities, but Comté, Beaufort, or a blend with sharp white cheddar can be substituted at a one-to-one ratio.
Storage
Refrigerator: 4 days — Cool completely and store promptly in an airtight container at or below 4°C (40°F) within two hours of preparation.
Freezer: 1 month — Wrap tightly in plastic wrap and heavy aluminum foil; freeze up to 1 month. Thaw overnight in refrigerator before reheating. Note that potato texture may soften slightly upon thawing.
Reheating: Transfer individual portions to an oven-safe dish and reheat in an oven preheated to 175°C (350°F), or microwave on medium-high power, until the internal temperature reaches at least 74°C (165°F) throughout as measured with a food thermometer.
Troubleshooting
The gratin sauce breaks into an oily, curdled liquid during baking
Cause: The oven temperature ran excessively hot, or lower-fat milk substitutes were used instead of heavy cream
Fix: Cannot be fixed once broken, but gently dabbing excess surface oil with a clean paper towel before serving will improve appearance
Prevention: Use heavy cream containing at least 35 percent milkfat and verify oven temperature with an oven thermometer at 190°C (375°F)
The potatoes and chard stems are still tough while the cheese topping is already dark brown
Cause: Vegetables were cut too thick or the dish was uncovered too soon during baking
Fix: Tightly re-cover the gratin with aluminum foil and continue baking at 190°C (375°F) for an additional 15 to 20 minutes until a knife inserts smoothly
Prevention: Slice potatoes strictly to 3 mm and chard stems to 5 mm, keeping the aluminum foil sealed tightly for the entire first 40 minutes
The gratin is loose and collapses into liquid when served onto plates
Cause: The dish was cut immediately while piping hot without allowing the setting rest period
Fix: Let the remaining gratin rest an extra 10 to 15 minutes in the dish so the starches reabsorb free liquids
Prevention: Adhere strictly to the 15-minute resting step at room temperature before cutting
Cultural Context
Originating in the historic Dauphiné province of southeastern France, gratins traditionally celebrate sliced root vegetables baked slowly in rich Alpine cream. French home cooks routinely practiced whole-plant thrift by incorporating chard ribs, known regionally as cardes, turning tough vegetable stems into delicate, succulent gems. This gratin bridges rustic farm frugality with classic French gratin technique.
