Homemade yoghurt

Ingredients

1 litre milk
6 heaped tablespoons dried milk powder
6 tbsp live, plain  yoghurt

Method

Boil a litre of milk (this kills any 'non-yoghurt bacteria' in the milk), then allow it to cool to about 45 degrees. Don't start making the yoghurt before the milk has cooled sufficiently, because the heat will kill the 'good bacteria'.
Now add the pot of live yoghurt and milk powder, stir it in
Cover the bowl with a lid or some cling film, wrap it in a towel and put it somewhere warm - in an airing cupboard or above a radiator are good places. Alternatively, you can pour the mixture into a warmed, wide-mouthed Thermos flask and seal.
I use a bowl placed over a pan off warm water, I just keep checking the water temp. Gently heat the water as necessary.
The process of yoghurt making takes 8-10 hours: too short and the yoghurt will be of a less thick consistency; too long and the curds and whey start to separate
If you’d like a thicker finish, you can strain the yoghurt through a muslin-lined sieve over a bowl in the fridge for a few hours.