1lb Broccoli (Florets cut off, stems sliced into 1/4 inch pieces)
Bring a pot of salted water to a rolling boil.
Cook the broccoli in the water until a paring knife will, with only a little resistance, pass through the broccoli when pressed against the side of the pot. It should make a distinct "tok" sound as the blade hits the metal. The broccoli should still be a fresh green color.
While saving the cooking water, remove the broccoli from the pot using a wire strainer or skimmer and place it in the bowl of a blender (preferably a high speed one, like a vitamix).
Pour enough of the cooking water into the blender to come halfway between the bottom and the top of the broccoli. You can always add more if it needs to be thinned. Blend on high speed until the soup is homogenized. Season with salt and pepper to taste.