How to Make It
Roast the peppers directly over a gas flame or under a preheated broiler, turning, until charred all over. Transfer the peppers to a large bowl, cover tightly with plastic and let cool completely. Peel, seed and stem the peppers, then cut them into 1/3-inch dice.
Meanwhile, in a small saucepan, combine the sugar with the water and cook over moderate heat without stirring until lightly golden in color, 3 to 5 minutes. Add the vinegar and cook until the caramel dissolves, about 1 minute; let cool completely.
In a large saucepan of salted boiling water, blanch the corn kernels and sliced leeks until crisp-tender, 3 to 5 minutes; drain well and let cool completely.
In a large bowl, toss the corn and leeks with the roasted peppers, scallions and sweet-tart dressing. Season the corn with salt and pepper, transfer to a platter and serve.