Peel and dice the potatoes and place them in a seven quart slow cooker with about two quarts of water.
Add the chopped onion and minced garlic. Salt and pepper to taste and add the chicken bouillon. At this point you may need to add more water. You want to just cover the potatoes and onion with liquid.
Cook for 3 to 4 hours on high.
The potatoes should be done.
Add the cheese and cover with the potato mixture so that it starts to soften and melt while you mix the milk and starch.
In a 1 to 1 & 1/2 quarts of water mix enough non-fat milk powder to make 3 quarts of milk. I recommend using a gallon container and a hand mixer for this part.
After you have gotten all the lumps out of the milk powder you can mix in the corn starch.
You may need to adjust the amount of corn starch depending on how thick you want the soup. Add the milk and suspended corn starch to your slow cooker and stir well.
Make sure that the cheese gets well mixed into your soup. Add more water to fill your slow cooker and make sure that everything is mixed well.
Replace the lid and cook on high for another 30 minutes.