Fold the foam slowly and gently into the egg-yolk base, sprinkling in the ground hazelnuts and the breadcrumbs as you go, taking care not to deflate the foam.
Pour into a buttered ring mold, cover (e.g. with parchment paper), and steam in a boiling water bath for about 30 minutes, until set.
Meanwhile, peel the oranges and cut into rounds.
Turn the cooked soufflé out onto a plate, shape a hollow in the center, and layer in the orange rounds, sprinkling each layer with sugar.
Whip the 5 egg whites into a stiff foam, mix in the vanilla sugar, and coat the whole soufflé with it.
Dry out in an oven at 150 °C for about 12-15 minutes (do not let it brown), until the foam is slightly dry on the outside.
Serve immediately; in summer, it can be made the same way with any other fruit.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.