Grease the recesses of a donut tray (for 12 pieces, each 7 cm Ø) well. Cream 3 eggs, sugar, vanillin sugar and salt. Stir in oil in a fine jet. Stir in yoghurt. Sift flour and baking powder over it and stir in briefly
Fill the dough almost halfway into the hollows. Chill the rest of the dough. Bake in a hot oven (electric range: 175 °C/circulating air: 150 °C/gas: level 2) for 15-20 minutes. Let cool down briefly. Remove donuts carefully and let them cool down. Clean the tray and grease approx. 8 cavities again. Bake the rest of the dough in the same way
Stir icing sugar, egg white and 3-4 tablespoons of water until smooth. Divide into 5 bowls. Colour with food colouring green, red, yellow and blue or brown with cocoa. If necessary, stir brown icing a little thinner with a few drops of water. Spread the donuts with it and let them dry.