Bring a large pot of water to boil and add a large pinch of salt.
Chop the clean broccoli head into florets.
Drop the florets into the pot, add another large pinch of salt, and cover the pot with its lid.
Boil the broccoli until the florets are easily pierced with a knife, about 4 minutes.
Drain the veggies, collecting the cooking water in a bowl.
Transfer the still-warm broccoli to a blender, then add the collected cooking water until the pitcher is about half full.
Secure the lid and pulse a few times to reduce the chance of the blender lid blowing off.
Switch the speed to high and blend until the mixture is thickened.
Season with salt and black pepper to taste.
