Gratins are basically nothing more than vegetables and cream baked together in a slow oven until they fuse. The vegetables soak up the liquid to the point that they become meltingly tender. The cream ennobles the essence of each vegetable. The crusty layer on top combines the best of both ingredients and gilds the dish with a lovely brown. No wonder gratins are so beloved.
But gratin lovers are a contentious bunch, willing to argue almost any point: the shape of the pan, the type of potato, the mixture of cream and milk. That’s odd, considering that the finished dish is such a paean to simple comfort and that it always seems to turn out perfectly, no matter what you do. I tested this dish with baking and boiling potatoes side by side and couldn’t tell the difference.
6 SERVINGS
1 |
tablespoon butter |
1 |
leek, white part only, chopped (about ¾ cup) |
¼ |
pound mushrooms (any type), sliced |
1 |
shallot, minced |
|
Salt |
1½ |
pounds potatoes, peeled |
1½ |
ounces Gruyère, grated (about ¼ cup) |
1¼ |
cups milk |
⅔ |
cup heavy cream |
Heat the oven to 400 degrees. Generously butter a heavy baking dish that is roughly 8 by 10 inches.
Melt the 1 tablespoon butter in a skillet over medium heat. Add the leek and cook until softened, about 5 minutes. Add the mushrooms and shallot and reduce the heat to low. Cook until the mushrooms begin to darken and give off their moisture, about another 5 minutes. Season with salt to taste.
Slice the potatoes very thinly and pat them dry with a kitchen towel. Arrange half of the potatoes in a rough layer in the baking dish, then distribute the leek and mushroom mixture over the top. Scatter half of the grated cheese over that and season with salt to taste. Top with the remaining potatoes in as solid a layer as possible. Scatter the remaining cheese over the top.
Bring the milk just to a simmer in a small saucepan and pour it over the potatoes. You should just barely be able to see the milk under the top layer. Pour the cream over the top and bake for 30 minutes. The milk should be puffed and bubbling and beginning to brown, and the potatoes should be starting to become tender. Bake for 25 to 30 minutes more, or until the top is thoroughly browned, the milk bubbles have subsided and the gratin is a compact mass. Remove from the oven and serve.