1 Line a sieve with a double layer of muslin. Combine 500g thick Greek-style yoghurt with 2 tsp salt in a bowl. Spoon yoghurt into sieve. Cover with plastic wrap and refrigerate overnight (preferably 2 nights) to drain all liquid from yoghurt. Discard whey.
2 Finely chop 1½ cups mixed herb leaves (flat-leaf parsley, thyme, dill and mint). Roll 2 tsp yoghurt into a ball. Roll in herbs and put in a sterilised jar. Repeat with remaining yoghurt and herbs. Cover balls with olive oil. Seal jar and put in the fridge for up to 1 week.