Add the entire 1/2 gallon of milk to saucepan and warm over medium heat. Stir regularly and check the temp consistently to keep from over-heating. It is a terrible mess if you forget about it and it boils over... Might want to stay close for this step.
Heat milk to a temperature of 180°F and then remove from heat immediately.
Let milk cool to 100°F and add the powdered culture or yogurt starter.
Transfer to mason jars and secure lids. It's a good idea to run your jars though the dishwasher prior to use to get them extra clean. A canning funnel can also be helpful for this step. I often spill a little milk getting it from pan to jar. Don't tell Priscilla!
Set up sous vide on 105°F and fill bucket with water. If you have the Rubbermaid 18 qt tub, add about 15.5qt to get your jars covered.
Set it and forget it! Let the sous vide do its magic for 24 hours and then the yogurt will be ready to eat!