Equipment
Ingredients
Vegetables
- 700 g yukon gold potatoes, peeled and thinly sliced to 2 mm
- 400 g zucchini, trimmed and thinly sliced to 3 mm
- 150 g yellow onion, peeled and thinly sliced
- 3 garlic, peeled and finely minced
Liquids and Seasonings
- 350 ml evaporated milk, canned, unsweetened
- 60 g parmesan cheese, finely grated
- 7 g fine sea salt, fine granulated
- 1 g ground black pepper, freshly ground
- ½ g ground nutmeg, freshly grated
- 1 g sweet paprika, ground dry
- 1 g dried thyme, crushed dry leaves
- 5 ml olive oil, liquid
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 243 kcal
- Protein
- 12 g
- Carbohydrates
- 31 g
- Fat
- 9 g
- Zinc
- 1.8 mg
- Water
- 207 g
Sources: Aggregated Public Data, USDA FoodData Central
Method
Preheat the oven to 190°C (375°F) with a rack positioned in the center.
Grease the bottom and inside walls of the 2-liter baking dish with 5 ml of olive oil using a pastry brush.
Slice the peeled Yukon Gold potatoes into uniform 2 mm thick rounds using a mandoline slicer, keeping them unrinsed to preserve surface starch.
Slice the trimmed zucchini into uniform 3 mm thick rounds using a mandoline slicer.
Slice the peeled yellow onion into thin half-moons approximately 2 mm thick using a chef knife on a cutting board.
Whisk 350 ml evaporated milk, minced garlic, 7 g fine sea salt, 1 g black pepper, 0.5 g ground nutmeg, 1 g sweet paprika, 1 g dried thyme, and 30 g of the grated parmesan cheese together in a mixing bowl until evenly incorporated.
Layer half of the sliced potatoes across the bottom of the greased 2-liter baking dish, shingle half of the sliced onions and half of the sliced zucchini on top, and pour half of the seasoned evaporated milk mixture evenly over the layers.
Arrange the remaining sliced potatoes, onions, and zucchini in tightly overlapping shingled rows over the first layer, pour the rest of the milk mixture over the surface, and scatter the remaining 30 g of grated parmesan cheese evenly over the top.
Cover the baking dish tightly with aluminum foil to trap steam, place it in the oven at 190°C (375°F), and bake for 40 minutes.
Remove the aluminum foil and bake uncovered at 190°C (375°F) for 20 minutes until the cheese is deep golden brown, the liquid is bubbling actively around the edges, and the center reaches at least 93°C (200°F) on a food thermometer.
Rest the gratin uncovered on a heatproof surface for 10 minutes at room temperature to allow the starch matrix to set and the liquid to thicken before slicing.
Chef's Notes
- Evaporated milk contains approximately 60 percent less water than regular milk, delivering rich dairy body and emulsifying proteins that resist curdling without the heavy butterfat load of heavy cream.
- Yukon Gold potatoes strike the optimal balance between starch and structure, providing enough released amylose to thicken the evaporated milk while holding clean slices when portioned.
- Shingling the vegetable slices in slightly overlapping vertical angles rather than laying them flat allows moisture to escape evenly, preventing trapped pockets of liquid under the zucchini.
- If you prefer a deeper, caramelized gratin crust, turn on the oven broiler for the final 2 minutes of the uncovered bake, watching continuously to avoid burning the parmesan.
Storage
Refrigerator: 4 days — Cool completely to room temperature within 2 hours of baking. Transfer to an airtight container or cover the baking dish tightly with wrap, and refrigerate promptly at or below 4°C (40°F).
Reheating: Reheat refrigerated leftovers in an oven preheated to 175°C (350°F) for 15 to 20 minutes until bubbling and heated throughout to a safe minimum internal temperature of 74°C (165°F) as verified with a food thermometer.
Troubleshooting
The gratin liquid appears watery rather than creamy after baking
Cause: The zucchini released excessive internal water or the potato slices were rinsed prior to assembly
Fix: Bake uncovered for an additional 10 minutes at 200°C (392°F) to evaporate excess water, then rest the dish for 15 minutes to let starches reabsorb the sauce
Prevention: Cut zucchini slices slightly thicker than the potatoes (3 mm versus 2 mm) and never rinse sliced potatoes in water so their natural starch thickens the sauce
Potatoes remain hard or crunchy in the middle after the full baking time
Cause: Potato slices were cut thicker than 2 mm or the foil was not sealed tightly enough, letting cooking steam escape
Fix: Cover the dish tightly with aluminum foil again, splash 30 ml of warm milk around the dry edges, and return to the oven at 190°C (375°F) for 15 minutes
Prevention: Calibrate the mandoline slicer to 2 mm thickness and crimp aluminum foil firmly around all dish edges during the initial 40-minute bake
The cheese top layer turns dark brown before the vegetable center is cooked through
Cause: The baking dish was placed too close to the upper heating element or the foil was removed prematurely
Fix: Tent a fresh piece of aluminum foil loosely over the dish to shield the browned cheese while finishing the center bake
Prevention: Bake exclusively on the middle rack and keep the foil sealed for the entire first 40 minutes of baking
Cultural Context
Originating in the historic Dauphine province of southeastern France, traditional gratin dauphinois relies on layered potatoes baked slowly in seasoned cream and scented with nutmeg. Adding summer vegetables such as zucchini and onions represents a sun-drenched Provencal variation that balances root vegetable heartiness with garden freshness. Utilizing evaporated milk modernizes the classic approach, preserving the signature silken custard while maintaining a lighter nutritional profile.
