gallon milk
cup yogurt (I have noticed that Axel Rod nonfat yogurt works very well but one can use any yogurt as long as it's fresh.)
Pour the milk into a pan and place over a medium heat. Bring the milk to boil while stirring. Once the milk starts boiling lower the heat and let it simmer for 10 more minutes, stirring occasionally. Meanwhile, leave the yogurt out to come to room temperature.

Remove the milk from the heat and let it sit untill it reaches a temperature of about 37oC or 99oF (Basically body temperature). The temperature is very important. If we add the yogurt while the milk is very hot the heat will kill the bacteria inside the culture and if it's too cold the bacteria will not grow. Pour the milk into a bowl. Mix the yogurt until smooth and creamy. Add the yogurt to the milk and stir. Cover the bowl and place it in a warm location. If you can't find one, heat your oven to 200oF. Place the bowl in the oven and turn the heat off. Keep the bowl in the oven over night or about 10 to 12 hours. In the morning the milk should have thickened and reached a custard-like consistency. Refrigerate for another 12 hours. Mix the yogurt until smooth and creamy. The yogurt is now ready to be consumed. Noosh-e Jan!

Remember it is very important to start with sweet, fresh yogurt otherwise the resulting yogurt will taste sour.