For the lemon roulade, first whip the egg whites and water until very stiff. Beat in the sugar and citroback. Stir in egg yolks, fold in mixture of cornstarch, flour and baking powder.
Spread the sponge mixture evenly on a baking tray lined with greased baking paper and bake in a heated oven for 12-15 minutes at 220-225 °C (gas: level 3-4).
For the filling, mix well Citroback, lemon juice, gelatine and sugar, leave to cool and set. Whip the cream until stiff and fold in, chill again.
Turn out the baked sponge cake onto a tea towel, peel off the paper, flatten and roll up with the help of the towel. When cool, roll back, spread with filling and roll up again.
Sprinkle lemon roulade with powdered sugar.