Rinse, clean and cut rhubarb into small pieces. Bring to the boil together with water, lemon zest and sugar.
Mix the pudding powder and both egg yolks with 2 to 3 tablespoons of cold water. Bind the boiling rhubarb liquid with it and bring to the boil briefly.
Beat the egg whites until stiff and fold them loosely under the rhubarb dish with a whisk. Then put in a glass bowl and let cool down.