In a 6- to 6-quart crockpot, combine potatoes, broth, celery, carrots, celery and onion with salt, garlic, parsley and pepper.
Cover the pan with a lid and cook for 8 or 4 hours on low, or until the vegetables are tender.
While the bacon is baking, place it flat on a baking tray and bake at 350 degrees for about 15-20 minutes, until you get the desired crispy texture. Transfer the bacon to a cutting board and let cool on a plate before you chop.
Make the roux in your microwave just before the soup is finished cooking.
Melt the butter in a large bowl or measuring cup. Do this for 30 seconds.
Mix in the flour and stir until it is completely absorbed.
Mix the milk into a bowl until it is smooth. Use a scraper for a clean edge.
Microwave at high for 45 seconds, whisking after each interval until thickened. I found that 4 times at 45 seconds worked well for me. It will bubble up so be sure to watch it in the microwave.
The thickened milk should be added to the crockpot along with 1 cup cheese and most of the chopped bacon.
Top the soup with any remaining cheese, bacon, and green onions.