If you don't have a yoghurt maker then you could use a wide - necked flask of some sort, or a jar, provided that you have somewhere consistently
warm to place it for 24 hours (like an
airing cupboard, or in the oven
with just the light on).
Alternatively, pour the mixture into a bowl, cover
with clingwrap and leave in a
warm place, such as the
airing cupboard or on a towel over a radiator.