Preheat the oven to 425°. Position a rack in the upper third of the oven. Generously butter a large rimmed baking sheet and dust generously with superfine sugar. In a large mixing bowl, using a handheld electric mixer, beat the egg whites until soft peaks form. Beat in the superfine sugar, 1 tablespoon at a time, beating well after each addition, until firm peaks form. In a bowl, whisk the egg yolks until pale yellow. Gently fold the egg yolks into the beaten whites.
With the spatula, use half of the egg mixture to form four 5-by-3-inch ovals on the prepared baking sheet. With the back of a spoon, make a 2-inch-long indentation in the center of each oval and fill with 1 tablespoon of the jam. Cover with the remaining egg mixture to enclose the jam.
Bake the soufflés for about 10 minutes, until puffed and golden brown but still slightly jiggly in the center. With a metal spatula, gently transfer the omelets to plates. Dust with confectioners' sugar and serve right away.