Equipment
Ingredients
Vegetable Base
- 30 ml olive oil
- 100 g shallots, finely diced
- 400 g cremini mushrooms, cleaned and thinly sliced
- 15 g garlic, minced
- 300 g kale or swiss chard, tough stems removed, leaves roughly chopped
Custard
- 6 eggs, large, room temperature
- 350 ml whole milk
- 15 g dijon mustard
- 6 g kosher salt
- 2 g black pepper, freshly ground
- 1 g nutmeg, freshly grated
Cheese & Finishing
- 150 g gruyere cheese, grated
- 50 g parmesan cheese, grated
- 15 g unsalted butter, softened, for greasing the dish
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 356 kcal
- Protein
- 22 g
- Carbohydrates
- 13 g
- Fat
- 25 g
- Fiber
- 3 g
- Sugar
- 6 g
- Sodium
- 822 mg
- Saturated Fat
- 11 g
- Trans Fat
- 0 g
- Monounsaturated Fat
- 10 g
- Polyunsaturated Fat
- 3 g
- Cholesterol
- 230 mg
- Potassium
- 722 mg
- Calcium
- 599 mg
- Iron
- 2.4 mg
- Magnesium
- 53 mg
- Phosphorus
- 483 mg
- Zinc
- 3.1 mg
- Vitamin A
- 330 mcg
- Vitamin C
- 49 mg
- Vitamin D
- 2.0 mcg
- Vitamin E
- 1.8 mg
- Vitamin K
- 200 mcg
- Vitamin B6
- 0.4 mg
- Vitamin B12
- 1.3 mcg
- Thiamin
- 0.21 mg
- Riboflavin
- 0.94 mg
- Niacin
- 3.3 mg
- Folate
- 83 mcg
- Water
- 224 g
Sources: USDA FoodData Central
Method
Preheat the oven to 190C/375F. Generously coat the inside of a gratin dish or baking dish with the softened butter.
Heat the olive oil in a large skillet over medium-high heat. Add the diced shallots and cook until softened and translucent, about 3 minutes.
Add the sliced mushrooms to the skillet. Let them sit undisturbed for 3 minutes to develop a deep brown sear, then stir and continue cooking until they release their liquid and the pan is completely dry.
Reduce the heat to medium. Stir in the minced garlic and chopped greens. Cook, tossing frequently, until the greens are completely wilted and tender. Remove from heat and allow to cool slightly.
Transfer the cooked mushroom and greens mixture into the prepared gratin dish, spreading it out into an even layer.
In a mixing bowl, vigorously whisk together the eggs, whole milk, Dijon mustard, salt, black pepper, nutmeg, and exactly half of both the grated Gruyere and Parmesan cheeses.
Pour the egg and milk custard evenly over the vegetables in the gratin dish. Sprinkle the remaining Gruyere and Parmesan evenly across the top.
Bake the gratin at 190C/375F for 35 to 40 minutes. The custard should be fully set with no liquid pooling, and the top should be crusty and golden brown.
Remove the gratin from the oven and let it rest for 10 minutes. This allows the custard to stabilize before slicing.
Chef's Notes
- To achieve a restaurant-quality sear on the mushrooms, avoid salting them until they are completely browned. Salt draws out moisture prematurely, leading to steaming rather than searing.
- A hint of freshly grated nutmeg is traditional in French egg and dairy preparations like quiche and gratin; it bridges the gap between the savory earthiness of the vegetables and the rich dairy.
- If you want to add a textural contrast, you can toss 30g of chopped walnuts or a handful of pumpkin seeds over the top during the last 10 minutes of baking.
- For deeper flavor development, the raw custard mixture can be prepared up to a day in advance and stored in the refrigerator, bringing it up to room temperature while you prep the vegetables.
Storage
Refrigerator: 3 days — Cover tightly with food wrap or store in an airtight container.
Freezer: 1 month — Wrap individual portions tightly. Texture of the greens may soften slightly upon thawing.
Reheating: Reheat gently in a 160C/320F oven for 15-20 minutes until warmed through to prevent the custard from splitting.
Troubleshooting
Gratin is watery or custard fails to set properly
Cause: Vegetables, especially mushrooms and greens, retained too much moisture before baking
Fix: Return to the oven for an additional 10 minutes; if the top is browning too quickly, tent loosely with aluminum foil.
Prevention: Ensure all liquid is cooked off during the sauteeing phase. If using frozen or very wet greens like spinach, thoroughly wring out excess liquid in a clean kitchen towel before adding to the pan.
Custard appears split, grainy, or weeping
Cause: Oven temperature was too high, causing the egg proteins to curdle and squeeze out liquid
Fix: Cannot be fixed once curdled, but still safe to eat.
Prevention: Check oven calibration and ensure it does not exceed 190C. Avoid substituting the whole milk with lower fat milk or water.
Cultural Context
The term gratin comes from the French word gratter, meaning to scrape or grate, originally referring to the crusty, delicious bits stuck to the pan. Originating in the Dauphine region of France, the technique of baking ingredients in a shallow dish under a golden crust of cheese and dairy has evolved to encompass a wide variety of comforting, rustic regional vegetable dishes.
