Scallion, Potato, and Herb Puree

Scallions come in many shapes and sizes, from tiny and red to thick and green and very, very long. A stack at the St. Paul market labeled "table onions" were nearly as long as King Alfred leeks and just as sweet. Potatoes are, of course, delicious with leeks, so you can expect they'd be good with scallions, and they're a perfect vehicle for herbs, whether bracing parsley, a handful of chervil, tarragon, or whatever herb you love.

It's completely optional, but I often add a little cheese—goat cheese or sheep's milk feta for a bit of tang, Gruyère for a richer version. Leftovers are delicious browned in clarified butter or olive oil. Measurements are flexible.

Ingredients

• 2 large (1 pound or a little more) russet potatoes

• 3 large leeks, white parts only

• 2 fennel bulbs, about 6 ounces each

• Sea salt and freshly ground pepper

• 1 1/2 tablespoons unsalted butter

• 1 bunch scallions, including an inch of the greens, sliced

• 1/4 cup chopped fennel greens or 2 tablespoons each chopped parsley and tarragon

• 1 teaspoon grated lemon zest

• 2 large eggs

• 1 1/2 cups milk or half-and-half

• 1/2 cup freshly grated Parmesan or Gruyère cheese

Instructions

1. Preheat the oven to 375 F. Lightly butter a 2-quart gratin dish. Chop the leeks into 1/2 inch pieces and wash them well in plenty of water, separating the rings. Let them soak while you trim and quarter the fennel. Slice it very thinly, including the core. Bring a skillet of water to a boil, add the fennel and a pinch of salt. Simmer until the fennel is translucent, about 2 minutes, then drain.

2. Melt the butter in a wide skillet. Lift the leeks out of their soaking water and add them to the pan along with the fennel. Season with 1 teaspoon salt and cook over medium heat, stirring frequently, until the leeks are tender, about 10 minutes, adding the scallions after 5 minutes. Add the fennel greens and lemon zest, taste for salt, and season with pepper. Scrape the vegetables into the prepared dish.

3. Beat the eggs and milk together and add 1/2 teaspoon salt plus the cheese. Pour it over the vegetables, then bake until the top is browned here and there in places, about 40 minutes. Let rest for a few minutes, then serve.

Variation with Endive: Slice or chop 1 or 2 white Belgian endives and cook them with the leeks and fennel.