Kale and leek gratin with Gruyère
30 – 40 Minutes
The secret to this crowd-pleasing gratin is its easy, classic cheese sauce. Known as sauce Mornay to generations of French chefs, it’s the same base used to make traditional mac n’ cheese, thickened with a roux (pronounced “roo”), a mix of butter and flour. The leeks and kale can be cooked the night before, covered, and refrigerated overnight; bring to room temperature while you make the cheese sauce.
In your bag
- 1¼ pounds leeks
- 1 pound kale
- Peeled fresh garlic
- 5 ounces Gruyère
- Fresh flat-leaf parsley
- 4 tablespoons unsalted butter
- ¼ cup all-purpose flour
- ¼ teaspoon nutmeg
- ½ teaspoon Urfa biber chile flakes (optional)
- 2 cups milk
- 2 tablespoons bread crumbs
- 1 ounce grated Parmesan
Prep the vegetables and herbs
Heat the oven to 450ºF.
- Trim the root ends from the leeks; cut the leeks in half lengthwise, then crosswise into ½-inch-thick half-moons. Soak the leeks in a bowl of cold water, allowing any dirt to settle at the bottom. Skim the leeks from the surface of the water and pat dry.
- Strip the kale leaves from their stems; coarsely chop the leaves.
Cook the leeks and kale
While the leeks and kale cook, start the cheese sauce.
Make the cheese sauce
- Finely chop enough garlic to measure 1 tablespoon.
- Using the large holes of a box grater, grate the Gruyère cheese.
- Strip the parsley leaves from their stems; coarsely chop the leaves.
Bake the gratin