Ingredients you will need: Whole milk, and 2 spoons of good plain yogurt for starter.
By "good", I mean yogurt that contains milk and cultures ONLY, without the additives, preservatives, fruits etc.
You will also need a kitchen thermometer. Temperature is important.
Start the night before,to finish next day. Unless your house is really warm or in the summer, when fermentation takes only 4-5 hours.
Here are the steps.
Bring milk to boil, and as soon as it starts rising pull off the stove. At this point the temperature is about 180 F.
Have your starter yogurt on the counter, let it reach room temerature.
Let milk cool down to 108- 115 degrees Fahrenheit.
Fill 1/2 glass with this boiled and cooled milk, and dilute the reserved yogurt/starter in it.
When well diluted, pour it back in the pot of milk.
Cover the pot with a clean towel, then fit the lid on.
Put the pot in the oven, and let it sit with the light on.
The yogurt will set in about 3 hours in the summer, and 8-10 in the winter.
Next empty the pot in a clean cloth-lined colander, and let the whey strain for 2-3 hour in the fridge.
You have just made excellent Greek yogurt!
Use it in all yogurt recipes.