In India, we all make our own yoghurt (even though many packaged varieties are easily available). Here's the simplest recipe --
Ingredients -- milk, a tablespoon or two of yogurt with live cultures (you can use regular plain store bought yoghurt for this, but not probiotic yoghurt)
Method --
* Gently heat the milk. The milk must at least reach 185° F for two minutes. The desirable temperature is 200° F. If the milk is not hot enough then the yoghurt will not be firm but will be stringy.
* Turn off the heat. Let it cool to tepid warm, cooling to 122° F but not below 105° F.
* Add starting culture. Mix well (I just pour the mixture from one bowl to the other till it looks mixed)
* Incubate in a warm place for 5 hours or depending on room temperature.
* Refrigerate when it looks set.
For more tips on the best dishes to make yoghurt in, its health benefits, and the negatives of eating store bought stuff, see
http://www.copperwiki.org/index.php/Yoghurt?utm_source=geetanjali_yahooanswers&utm_medium=email&utm_campaign=invite