Leek and Spring Onion Gratin

Preparation

1. Step 1

   Place a rack in the top third of oven and heat to 400 degrees. In a medium bowl, toss scallions, green garlic, salt and pepper.

2. Step 2

   Heat a 12-inch cast-iron skillet over medium heat. Arrange the leeks cut-side down in the skillet, then scatter spring onions in the gaps. Sprinkle a little more salt on top, then spread scallion mixture in an even layer in pan. Pour in ¼ cup water and top with butter.

3. Step 3

   Cover and and simmer on low heat until vegetables are soft, 20 to 25 minutes.

4. Step 4

   Uncover the pan, turn heat to medium-high and cook until liquid is evaporated and edges are starting to brown and sizzle, 5 to 10 minutes longer.

5. Step 5

   Meanwhile, in a small bowl, rub together anchovies, Parmesan, panko, thyme, lemon zest and red pepper flakes. Drizzle in oil and toss to combine.

6. Step 6

   Sprinkle Gruyère evenly into skillet over leeks, pour in cream, then top with the bread crumb mixture. Drizzle with a little more oil. Transfer to oven and bake until golden and bubbly, 15 to 20 minutes. Cool slightly, then serve warm.