For the tzatziki, strain the yogurt in a dish towel to drain the whey.
Peel and grate the cucumber and drain in a colander. Mix garlic, salt, yogurt and vinegar well, add the cucumbers.
Stir butter or oil into the tzatziki. Garnish with cucumber slices in a bowl and place in the refrigerator to firm up a bit.
Preparation Tip:
If you like it a little milder and creamier, make the tzatziki with half sour cream and half yogurt.