Heat butter and coconut oil in a large saucepan.
Add carrot, celery, and onion and cook until vegetables just begin to brown.
Add broth, water, salmon, cauliflower, chives, garlic powder, and pepper.
Cover and cook on simmer until salmon is just cooked through.
Remove salmon to a cutting board and flake into pieces.
Meanwhile, scoop out most of the cauliflower (you can leave some florets in the chowder) along with a bit of the broth.
Transfer to a blender and blend until smooth.
Return the mixture to the pot and add the dill and mustard.
Mix well and serve.