Sharp Cheddar Soufflé

Wash your hands and clean the work surface. Position an oven rack in the lower third of the oven, leaving plenty of clearance above it, and preheat to 375°F. Coat the bottom and sides of the soufflé dish with 1 tablespoon of the softened butter. Place the dish on the baking sheet.

Prepare the salad before handling the eggs. Separate the lettuce leaves, discard damaged areas, and rinse the leaves under running water. Spin thoroughly dry, tear into bite-size pieces, and refrigerate in the salad bowl. In a small bowl, whisk together the olive oil, lemon juice, and the salad dressing’s 1/4 teaspoon salt. Set the dressing aside.

Grate the cheddar. Place the egg yolks in one bowl and the whites in a large, clean, grease-free mixing bowl. Keep all traces of yolk out of the whites. Wash your hands after handling the raw eggs.

Melt the remaining 4 tablespoons butter in the saucepan over medium-low heat. Whisk in the flour and dry mustard. Cook for 2 minutes, whisking continuously, until the roux is smooth and gently bubbling but has not browned.

Gradually whisk in the milk, adding a small splash first and whisking smooth before adding more. Increase the heat to medium and bring to a gentle simmer, whisking continuously. Cook for 3–4 minutes, until the white sauce is thick, glossy, and lump-free; the whisk should leave a brief trail across the bottom of the pan.

Remove the saucepan from the heat. Stir in the cheddar in several additions until melted, followed by the remaining 1/2 teaspoon salt and the black pepper. Let cool for 5–8 minutes, until warm but no longer steaming. Whisk in the egg yolks one at a time, incorporating each completely. Transfer the mixture to a large mixing bowl.

Using clean, dry beaters, beat the egg whites on medium speed until foamy, then increase to medium-high. Stop when they form glossy, firm peaks: a lifted peak should stand upright with just a slight bend at its tip. The whites should not look dry or clumpy.

Stir about one-quarter of the whites into the cheese mixture to lighten it. Fold in the remaining whites in two additions using the flexible spatula. Cut down through the center, sweep along the bottom, and lift the mixture over itself, rotating the bowl between strokes. Stop when no obvious white streaks remain. Scrape all the batter into the prepared dish and gently level the surface without pressing out the air.

About 5 minutes before the expected end of baking, whisk the dressing again, toss it with the lettuce, and divide the salad among four plates.