In a 6 qt pot, place the cauliflower, about 6 cups of water (enough to cover the cauliflower), and the kombu. Bring to a boil over medium-high heat, reduce to a simmer, and cook until very tender (about 15 minutes).
Turn off the heat. Remove the kombu and discard. Using an immersion blender, puree the cauliflower and water until completely smooth (carefully--it might splash and burn!). Season with salt to taste.
Turn the heat back on to medium-low. Add about 1-2 more cups of water, if desired, to bring to a "chowder" consistency. Add the potatoes, corn, garlic powder, and simmer until the potatoes are cooked through.
Turn off the heat, and stir in the milk/cream. Add more salt to taste. Serve garnished with pepper and chives.
This recipe is very forgiving; you can really adjust the amount of cauliflower, liquid, corn, and potatoes to suit your liking. You can use half and half or cream, but it won't be vegan.