Place the chicken broth, water, diced yellow onion, cauliflower florets and salt into the Instant Pot. (See post above for details on how to cut a head of cauliflower)
Cook on Manual HIGH for 4 minutes. Quick release the pressure.
Blend the cauliflower & broth mixture. This can be done by using an immersion blender or by transferring to a blender. If transferring to a blender, return to the Instant Pot after blending.
With the Instant Pot on keep warm, slowly whisk in the heavy cream.
Add the yellow mustard.
Slowly whisk in the cheese.
Taste test and add more salt if needed.
Serve immediately and garnish with extra cheese, bacon bits and chives if desired.
Stovetop Instructions: Simmer the broth, water, onion, cauliflower and salt for 15 minutes then follow directions starting on #3.