Pour the 1/2 gallon of milk into the slow cooker (I have used what I think is a 3 quart slow cooker, and there wasn't much wiggle room, but it worked. I've also used a 5 quart).Cook on low for 2 1/2 hours to 180 degrees (I never worry about the temperature, but in case you want to know).Turn off the slow cooker, and let the warm milk sit for another 3 hours, keeping the lid on the slow cooker (cooling to 110-115 degrees).Take 2 cups of the milk out and mix it with the yogurt.If you are thickening your yogurt with dried milk, you can add it at this time to the yogurt mixture.Combine the yogurt mixture with the milk in the slow cooker and whisk until smooth.Turn on the light in your oven.Insert slow cooker into the oven with the lid on. DO NOT turn on your oven. The oven light will provide warmth for your yogurt cultures.Leave in the oven for 8-12 hours.Add your favorite toppings.Store in the fridge for up to two weeks.