Don’t tell your guests how you make this—it requires a horrifying amount of heavy cream—until they have eaten it. It’s so good that they will no doubt ask for the recipe. If you want to avoid using so much cream, you can also make it with béchamel sauce.
1½cupsheavy cream or more as needed
Preheat the oven to 375°F. Prepare the leeks as shown. Place the leek halves, flat side up, in a gratin dish or baking dish in a single layer and pour over enough cream to come halfway up the sides.
Season with salt and pepper and cover loosely with aluminum foil.
Bake for about 30 minutes, or until the cream begins to thicken. Remove the foil and bake for 5 to 10 minutes more, or until the cream is very thick but not oily and is lightly browned. Serve right away on warmed plates.
How to Make Leek Gratin
Cut off the greens, leaving about 1 inch of green attached to the white. Cut off the hairy root end.
Wittle off the outer green from the end of the leek white.
Cut the white in half lengthwise. Rinse under running water with the root end up.
As you rinse, leaf through the membranes to release any sand.
Arrange leek halves in a baking dish in a compact but single layer and pour over the cream. Season with salt and pepper.
When you press on the leeks with a fork, the cream should barely cover the leeks. Cover with foil and slide the dish into a 375°F oven.
As the leeks brown, push the brown parts down into the cream (shown without foil).
When there is no liquid cream left, the leeks are ready. Serve from the baking dish.