Sliced leeks are cooked in butter for 8 to 10 minutes first, so they go into the dish already soft and sweet.
The bread, leeks, most of the Gruyère and the parsley are soaked in an egg, milk and cream custard seasoned with Dijon, then topped with the rest of the cheese and baked.
How to Make It
Dish buttered
Heat oven to 350°F and butter a 9-by-13-inch baking dish.
Leeks softened
Melt unsalted butter in a skillet. Cook the sliced leeks 8 to 10 minutes until soft.
Custard whisked
Whisk large eggs, whole milk, heavy cream, Dijon mustard, kosher salt, and black pepper.
Soaked
Place the bread cubes, cooked leeks, 1 cup Gruyère cheese, and chopped fresh parsley in the baking dish. Pour over the egg mixture and press gently so the bread absorbs the custard.
Topped and baked
Rest 15 minutes, top with the remaining 1/2 cup Gruyère cheese, and bake 40 to 45 minutes.
Rested
Rest 10 minutes before cutting.
What Goes in the Dish
Built in the baking dish, bottom to top.
Top
The last half cup of Gruyère, added after the 15-minute soak.
Custard
Eggs, milk, cream, Dijon, salt and pepper poured over and pressed in.
Leeks, cheese and parsley
The softened leeks, one cup of Gruyère and the parsley tucked among the cubes.
Bread cubes
Ten cups of day-old crusty bread spread over the buttered dish.
Ingredient Notes
- Leeks
- Two medium, white and light-green parts only, rinsed well after slicing.
- Gruyère cheese
- One and a half cups, one cup inside and half a cup on top.
- Day-old crusty bread
- Ten cups of 1-inch cubes.
Success Tips
- Rinse the sliced leeks in a bowl of water; grit settles to the bottom.
- Press the bread down gently so every cube touches custard.
- Check the center with a thermometer for 160°F before it comes out.
Why This Recipe Works
- Day-old bread absorbs custard without collapsing.
- Pre-cooking the leeks removes their raw bite and extra water.
- A 15-minute soak before baking lets the custard reach the center.
- Holding back half a cup of Gruyère gives the top its melted crust.
Serving Ideas
Cut into squares and serve warm with a green salad, or alongside roast chicken.
Storage and Reheating
Refrigerate
Refrigerate within 2 hours and keep up to 4 days; reheat portions to 165°F.
Frequently Asked Questions
Is this a dessert?
No, it is a savoury bake with leeks, Gruyère and mustard.
How do I know it is set?
The center reaches at least 160°F and the top is golden.
