Remove the skin from the onion, chop finely and sauté in a frying pan with half of the light butter.
Peel, rinse and grate the potatoes, add to the frying pan and continue to cook until the potatoes are done. Remove the frying pan from the stove.
Using two teaspoons, remove small balls in portions, shape into small Rösti valleys and fry with the remaining light butter until golden brown on each side.
Mix crème fraîche with the juice of half a lemon, fold in the tzatziki and spread the amount on the hash browns.
Garnish with olives.