Start by bringing sugar, water and a little corn syrup to a boil in a small saucepan. Cook it until the temperature reaches 235 to 240 degrees on a candy thermometer. This is called the "soft-ball" stage because if you drop a little of the syrup into a glass of water, it will form a soft, pliable ball (I've seen Jacques Pépin test this with his bare fingers; for the rest of us mortals, a candy thermometer is definitely preferred).
It'll take 10 to 15 minutes to cook the sugar down. Once the mixture becomes clear -- there is no sugar visible in the water -- stop stirring. Sugar cooked to these concentrations is prone to crystallize, and once this starts, things go bad really quickly, like the Ice-9 in Kurt Vonnegut's "Cat's Cradle." Adding a little corn syrup will reduce the chances of this, but it can still happen if you're sloppy. Brush the sides of the pan down with a little water if you see crystals forming there.
The good news is that the syrup cooks by itself without much checking from you. So while it is boiling, beat the egg whites to stiff peaks. Remember, you want to whip them long enough that when you lift the beater, you get a sharp point that doesn't fall over. Don't over-beat, though, or the egg whites will turn grainy.
When the egg whites are stiff and the syrup is done, leave the mixer running and slowly pour the syrup down the side of the mixing bowl (if it hits the beater, you'll get gummy sugar strings).
This is one of the coolest things in cooking: The egg whites, which look airy and delicate at first, will billow and swell enormously and turn snowy white with a texture like the inside of a s'more.
Keep beating until the outside of the mixing bowl is cool to the touch, another three to five minutes. Then fold in the fruit base and the whipped cream. Freeze and that's it.
Each of these techniques has its own qualities and there is no right or wrong answer when it comes to which you choose.
In developing these recipes, I chose blackberries for the Italian meringue soufflé, focusing on the sharp, bright side of their flavor. But you could just as easily pair them with the custard soufflé, and the result would be more about contrasting that flavor with the richness of the egg yolks.
The same is true of the peach soufflé. I chose the custard base for this and the result is subtle, a delicate peaches-and-cream start followed by a haunting aroma of fruit that lingers. Made with the Italian meringue base, the flavor would have been much simpler and pure "peachier."
Of course, you can also substitute whichever ripe seasonal fruit you prefer in either soufflé. Just remember that you'll need about 2 cups of it after cooking and straining. Whoever heard of something so elegant being so accommodating?