Turn your crockpot on low to let it heat up.
Pour your milk into a saucepan and heat over medium heat, stirring occasionally until it reaches 185 degrees. Use a candy or meat thermometer to check temperature.
Once milk reaches 185 degrees (bubbling, not boiling) remove from burner and place the pan in a sink half full of cold water. The water should only go up the sides about half way. Just make sure no water gets into the pan.
Let the milk cool down, stirring occasionally. Once milk has reached between 90 and 100 degrees, remove pan from water.
Measure yogurt starter (the ¼ cup of yogurt) into a bowl and pour about a cup of the warm milk over it and stir together. Meanwhile pour remaining milk into heated crockpot. Pour milk and yogurt from bowl into the crockpot and stir it all together.
Put the lid on, turn off, and unplug the crock pot. Wrap a heavy towel around it. Let sit for 6-10 hours.
After the yogurt has finished culturing, place the crock in fridge to cool yogurt. This will help the yogurt to set better.
Once cooled and set, scoop into smaller jars to store in the fridge. Should keep for 7-10 days.