To start, combine cream + butter + sea salt + crushed red pepper + black pepper + finely diced white onion in a medium soup pot over medium/medium-high flame.
Bring the cream mixture to a low simmer, stirring occasionally (1-2 minutes).
Reduce flame to medium/medium-low, add diced (1/2" cubed) fresh cauliflower. Simmer for 10 minutes, continuing to stir occasionally. (NOTE :: The cream should NOT be boiling. Boiling without a roux in the base can cause the cream to break, yielding a grainy texture.)
While the cauliflower and cream mixture is at a LOW simmer, microwave frozen broccoli florets for 1-2 minutes (just until warm).
Drain the warmed broccoli and chop into 1/2" pieces.
Add (chopped and drained) broccoli + dijon mustard to the cauliflower cream mixture.
Reduce flame to LOW stirring continuously (1 minute) until broccoli is warmed through.
Next, add shredded sharp cheddar + shredded parmesan.
Continue simmering and stirring continuously on LOW for 1-2 minutes (the soup should be simmering, NOT boiling).
Remove from flame, cover and allow to sit for 5 minutes while cheeses continue to melt.
Stir and serve.
* depending on desired consistency, you may wish to thin the soup slightly using water.