From America's Test Kitchen
“Chilled lemon soufflé” can be interpreted in many ways, from cooled baked pudding cake to lemony, eggy foam. But no matter what the desired outcome, what typically results is a dense, rubbery mass or a mouthful of tart egg white foam. The delicate balance of ingredients is hard for home cooks to get right. We wanted to perfect the unusual marriage of cream and foam, sweet and sour, high lemony notes and rich custard.
A starting point of egg whites, gelatin, sugar, and lemon juice had none of the creaminess we desired, so we cooked a custard base of milk, egg yolks, and sugar, adding a little cornstarch to prevent the yolks from curdling. To our custard we then added lemon juice and gelatin (to stabilize the mixture so it would set up while chilling). Because this was to be a soufflé, not a pudding, we lightened the custard with whipped cream and beaten egg whites. The egg yolks and dairy tended to mute the lemon flavor, so for more citrus punch we included grated lemon zest. Now we had the balance of flavor and texture that we sought: a satisfying but light custard with bright lemon flavor.
Serves 4 to 6
To make this lemon soufflé “soufflé” over the rim of the dish, use a 1-quart soufflé dish and make a foil collar for it as follows: Cut a piece of foil 3 inches longer than the circumference of the soufflé dish and fold it lengthwise into fourths. Wrap the foil strip around the upper half of the soufflé dish and secure the overlap with tape. Tape the collar to the soufflé dish as necessary to prevent it from slipping. Spray the inside of the foil collar with vegetable cooking spray. When ready to serve, carefully remove the collar. For those less concerned with appearance, this dessert can be served from any 11/2-quart serving bowl. For best texture, serve the soufflé after 11/2 hours of chilling. It may be chilled up to 6 hours; though the texture will stiffen slightly because of the gelatin, it will taste just as good.