Step 1: Ingridients
4 Cups of Milk
2 Cups of Cream (Half and Half works too)
4-5 Tablespoons of already made yogurt
A glass vessel that can hold about 6 cups of yogurt
Step 2: Sterilize
Step 3: Wait
During this time, it would be a good idea to clean your storage vessel(s).
Step 4: Oven and yogurt
Slowly bring your yogurt up to temperature (as not to shock any of the bacteria) - you can do this by adding a little warm milk, stirring - then adding more milk. Repeat.
Mix your yogurt into your milk for about two minutes to make a homogeneous mixture. Having it perfectly blended isn't super important, but it does speed the process along.
Then, pour your mixture into your glass storage vessel. Place in your oven (bottom rack) and allow to sit for about 4 hours. If you preheated to 200, turn your oven off once you've placed your container inside.
Step 5: 4 Hours Later
As I'm typing this, it shows the yogurt I made did not kill me.