Whisk eggs, sugar, vanillin sugar and salt with the whisk of the hand mixer for about 5 minutes until thick and creamy. Stir in oil in a thin stream. Stir in yoghurt. Mix flour and baking powder, stir in briefly. Grease the depressions of a donut tray (12 depressions, 7 cm Ø per depression) well.
Pour in dough until just over half of it. Put the rest of the dough in a cool place. Bake in a preheated oven (175 °C/ convection oven: 150 °C/ gas mark 2) for 15-20 minutes. Allow to cool briefly, then carefully remove the donuts. Let them cool down on a cake rack. Wash and dry the donut tray, grease 8 troughs and spread the remaining dough in them, bake in the same way. Sift icing sugar, stir with egg white and 3-4 tablespoons of water until smooth. Spread the icing on 5 bowls. Colour the icing green, red, yellow, blue and brown with food colouring and cocoa.
Wash and dry the donut tray, grease 8 troughs and spread the remaining dough in them, bake in the same way. Sift icing sugar, stir with egg white and 3-4 tablespoons of water until smooth. Spread the icing on 5 bowls. Colour the icing green, red, yellow, blue and brown with food colouring and cocoa. If necessary, stir the brown icing with a few drops of water until it is a little thinner. Spread the doughnuts with it, let them dry