Directions
Step 1
Separate the eggs while still cold; set aside to come to room temperature, about 30 minutes.
Step 2
Rinse the lemons and dry them thoroughly, then zest them with a microplane grater. You should have a generous tablespoon of zest. Juice the lemons; you should have a generous cup of juice. Some pulp is fine to leave in but remove any seeds.
Step 3
Whisk the egg yolks in a heavy-bottomed saucepan, then whisk in 1/2 cup sugar; add the lemon juice and zest, flour, vanilla, and salt.
Step 4
Place the saucepan over medium heat and bring the mixture to a very low boil, whisking constantly. Cook for 2 minutes to activate the flour, lowering the heat if necessary to prevent a rapid boil. The curd should be thick enough to coat the whisk.
Step 5
Off the heat, slowly whisk in the olive oil and continue whisking until completely blended. Allow the curd to come to room temperature before proceeding. (Pour it into a glass bowl, cover, and refrigerate if making in advance).
Step 6
When the lemon mixture has cooled, preheat your oven to 375°F with a rack in the center position. Prepare four 8-ounce ramekins by brushing the inside surfaces with the butter and then dusting each with a scant tablespoon of sugar. Invert each ramekin and tap on the bottom to remove any excess sugar; set them aside.
Step 7
Whip the egg whites on low speed for 1 minute to break them up, then add the remaining 4 tablespoons sugar and the cream of tartar. Increase the speed to high and whip until firm peaks form, about 5 minutes.
Step 8
Using a spatula, fold 1/4 of the egg whites into the lemon curd to loosen it, then fold in the rest of the whites in a gentle motion to avoid deflating them. When only a few streaks of curd remain, spoon equal amounts into the ramekins; the mixture should almost reach the rim. Smooth the tops with a small offset spatula.
Step 9
Place the ramekins on a rimmed sheet pan and place the pan in the oven. Bake until the soufflés rise an inch or so above the rims of the ramekins and the tops feel firm to the touch, about 15 to 20 minutes, depending on your oven. Serve within 5 minutes with a drizzle of olive oil, a dusting of confectioners’ sugar, and a dollop of whipped cream, if desired.