Here is what I do:
Pour 2 quarts of milk (I used 2%) into a large glass container.
Microwave, stirring several times, to a temperature of 180 degrees. (It takes about 15 minutes in my microwave)
Allow the milk to cool to 110 degrees.
Pour a small amount of the cooled milk into a small bowl and whisk in 2 tsps. Greek Yogurt starter that you have purchased or saved from a previous batch.
Whisk into the large container of milk.
Cover with a lid. Wrap the container of yogurt in a thick blanket or quilt. Preheat oven to 350 degrees for one (1) minute and turn off. Turn on the oven light. Place the wrapped container of yogurt in the back corner of oven near the light bulb. Close oven door and allow yogurt to do its thing.
I wait 10 hours. Remove yogurt container from oven. It will be thick with some liquid puddling on top. This is whey that will be strained off to create a thick Greek-Style product. I gently pour off the whey and then carefully pour the yogurt into a colander that has been lined with several coffee filters. Allow the yogurt to drain for several hours in the refrigerator or even over night.
Discard whey and whisk the yogurt until creamy. If desired, add vanilla extract and sweetener. Personally, I prefer mine a little sweet but John likes his with just vanilla.
Be sure to set aside a couple teaspoons before adding vanilla or sweetener as a starter for your next batch.