This is how I make it (although not very often, and without an easiyo thing):

1 litre milk
2 tablespoons plain yoghurt

Bring milk to the boil, turn heat down when it starts to rise up and simmer for 2 minutes.
Take off the heat and leave to cool to around 43C. (I use my candy thermometer)
Skim off the skin and beat the plain yoghurt with a little of the warm milk.
Beat in the rest of the milk. (Don't mix it in the pan you heated the milk in, as more often than not, there will be browned milk on the bottom of the pan, resulting in brown patchy yoghurt).
Pour into a 1 litre container (I use an old yoghurt tub!), or smaller containers and put lids on.
Wrap in towel and leave overnight to set. (I wrap in a towel and put into an insulated lunch bag/esky thing).
Place in the fridge and will be ready to eat after 8 hours.

Can use sheep or goat milk if you wish, and apparently skim milk too.
From Best Recipes website.

You can freeze the 'starter' yoghurt and let it defrost in the fridge when you are ready to make your next batch. It's very tart in taste (as you can imagine), so adding fruit or honey (or natural honeycomb) make great sweeteners, and maybe a little vanilla. It is very easy. And very thick. The trick with it is to make sure it cools down REALLY slowly, hence the insulating with towels.