Step 1

Position a rack in the upper third of an oven and preheat to 400°F. Coat a 14-inch oval gratin dish or large soufflé dish with the 2 Tbs. butter and sprinkle the bottom and sides with 1/2 cup of the cheese.

Step 2

In a large fry pan over medium heat, warm the olive oil. Add the leeks and thyme and cook until the leeks are tender, about 12 minutes. Season with salt and let cool.

Step 3

In a heavy saucepan over medium heat, melt the 5 Tbs. butter. Add the flour and whisk for 1 minute until combined. Whisk in the half-and-half and cook, whisking, until the sauce is smooth and thick, about 4 minutes. Transfer to a bowl. Stir in the egg yolks, one at a time. Stir in the remaining 1 1/2 cups cheese and the leeks. Season with salt and pepper.

Step 4

In a large bowl, beat the egg whites until stiff peaks form. Using a rubber spatula, fold one-fourth of the whites into the leek mixture. Quickly fold in the remaining egg whites until no white streaks remain. Pour into the prepared dish. Bake until the soufflé is golden brown, about 25 minutes. Serve immediately. Serves 6 to 8.

Step 5

Adapted from Williams-Sonoma Cooking from the Farmers’ Market, by Tasha DeSerio & Jodi Liano (Weldon Owen, 2010).