Once the broccoli and potatoes are soft, cover and simmer on low for six to seven hours, or high for three to four hours.
If desired, puree the soup:
Make the soup as smooth or thick as you want by blending it with an immersion blender. Another option to get a thicker consistency is to pour half of the soup into a blender, process until smooth, and then pour back into the crockpot.
Mix in the shredded cheddar cheese and heavy cream (or milk). Once the cheese has melted and the soup has thickened, continue cooking on Low for another 10 to 15 minutes, stirring once or twice.
To serve, spoon the soup into individual bowls and top with chopped parsley or chives, if preferred.
On cold days, warm up with a bowl of this cozy potato, broccoli cheddar soup.