Prepare your crock pot by plugging it in and setting it to low heat.
In a large bowl, combine the broccoli florets, chopped onion, and minced garlic. Add to the crock pot.
Pour the vegetable or chicken broth over the broccoli mixture.
Add the salt, pepper, and nutmeg (if using). Stir gently to combine.
Cut the butter into small pieces and add it to the crock pot.
Cover the crock pot and cook on low for about 4 hours, or until the broccoli is tender.
In a small bowl, mix the flour with a bit of milk to create a smooth paste. Add the remaining milk to the crock pot.
Use an immersion blender to blend the soup until smooth (or transfer to a blender and puree in batches).
Stir in the shredded cheddar cheese until melted and well incorporated.
Taste and adjust seasoning if necessary. Serve hot and enjoy!