Equipment
Ingredients
Vegetables
- 1000 g waxy potatoes (yukon gold or charlotte), peeled and sliced 3mm thick
- 200 g fresh sorrel leaves, washed, stems removed, shredded
- 1 garlic clove, halved
Custard Base
- 4 large eggs
- 250 ml whole milk
- 100 ml heavy cream
- nutmeg
- 6 g salt
- black pepper
Cheese & Finish
- 150 g gruyère cheese, grated
- 20 g unsalted butter, softened
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 418 kcal
- Protein
- 18 g
- Carbohydrates
- 39 g
- Fat
- 22 g
- Fiber
- 7 g
- Sugar
- 5 g
- Sodium
- 667 mg
- Saturated Fat
- 12 g
- Trans Fat
- 0 g
- Monounsaturated Fat
- 6 g
- Polyunsaturated Fat
- 2 g
- Cholesterol
- 182 mg
- Potassium
- 1219 mg
- Calcium
- 376 mg
- Iron
- 1.9 mg
- Magnesium
- 93 mg
- Phosphorus
- 421 mg
- Zinc
- 1.6 mg
- Vitamin A
- 632 mcg
- Vitamin C
- 52 mg
- Vitamin D
- 1.6 mcg
- Vitamin E
- 0.7 mg
- Vitamin K
- 2 mcg
- Vitamin B6
- 0.1 mg
- Vitamin B12
- 0.9 mcg
- Thiamin
- 0.06 mg
- Riboflavin
- 0.33 mg
- Niacin
- 0.1 mg
- Folate
- 21 mcg
- Water
- 81 g
Sources: Aggregated Public Data, USDA FoodData Central
Method
Preheat the oven to 180°C/355°F. Rub the inside of the baking dish vigorously with the cut side of the garlic clove, then grease generously with the softened butter.
Peel the potatoes and slice them into uniform rounds approximately 3mm thick. Do not rinse the slices after cutting, as the starch helps bind the layers.
Wash the sorrel, remove tough central ribs, and slice into ribbons (chiffonade). In a bowl, whisk together the eggs, milk, cream, salt, pepper, and nutmeg until fully combined.
Arrange a layer of potato slices in the bottom of the dish, slightly overlapping. Scatter a handful of sorrel ribbons and a sprinkling of grated Gruyère over the potatoes. Repeat this layering process until all vegetables are used, finishing with a neat layer of potatoes topped with the remaining cheese.
Slowly pour the egg and milk mixture over the layered potatoes. Tilt the dish gently from side to side to ensure the liquid penetrates to the bottom layers. Press down gently with a spatula.
Bake in the preheated oven for 45-50 minutes. The top should be deep golden brown, and a knife inserted into the center should meet no resistance from the potatoes.
Remove from the oven and let rest for at least 15 minutes before slicing. This resting period is critical for the custard to set so it can be sliced like a pie.
Chef's Notes
- Sorrel has a distinct lemony tang due to oxalic acid. If you find pure sorrel too intense, mix it 50/50 with fresh spinach.
- Waxy potatoes hold their shape, giving this dish its 'pie' structure. If you use starchy potatoes (like russets), it will be delicious but much softer and harder to slice cleanly.
- Do not rinse the potatoes after slicing. The surface starch is essential for binding the layers together with the egg custard.
- This dish is excellent served warm or at room temperature, making it perfect for lunch buffets.
Storage
Refrigerator: 3 days — Reheat gently to prevent eggs from becoming rubbery.
Freezer: 1 month — Texture of potatoes may change slightly upon thawing.
Reheating: Cover with foil and bake at 150°C/300°F until warmed through.
Troubleshooting
The gratin is watery when sliced
Cause: The sorrel released too much liquid or the dish didn't rest long enough
Fix: Let it cool longer; the liquids will reabsorb as the starch sets
Prevention: Ensure the sorrel is spun dry after washing; always rest the dish for 15+ minutes
Top is burning before potatoes are soft
Cause: Oven rack too high or temperature calibration off
Fix: Cover loosely with aluminum foil and continue baking until tender
Prevention: Bake in the middle or lower third of the oven
Cultural Context
Sorrel (Oseille) is a beloved herb in French cooking, particularly in the spring and autumn. While often paired with salmon, its use in potato gratins is a rustic farmhouse tradition where the herb's acidity balances the heavy dairy, much like lemon juice would in other cuisines.
