Bring a large pot of water to a boil over medium-high heat.
Chop the cauliflower into medium-sized florets by slicing the head of cauliflower down the middle, removing the steam, then separating the florets.
Chop the onion and garlic, sauteeing them in an a small pan over medium heat with two tablespoons of olive oil. This will take about 5 minutes until they are very fragrant and slighly translucent. Set aside.
Add the florets to the boiling water, adding the two tablespoons of coarse sea salt to flavor the water. Boil for about 10 minutes or until the florets are fork-tender.
Once the florets are fork-tender, drain them, then add them straigh back into the hot pot.
Add the heavy cream, butter, onions, and garlic to the florets.
Using an immersion blender pulse and blend the mixture until fully combined and smooth to your desired texture.
Taste the mixture, seasoning with salt and pepper as you desire.
Add in the fresh herbs, red pepper flakes, or other seasonings if using.