Place the cauliflower in a steamer basket set over a deep pot of simmering water and cover. Steam the cauliflower until it is just tender, about 15 minutes. Stick the tip of a sharp paring knife in the thickest part of the stem of the cauliflower to check for doneness. The timing depends on the size of the cauliflower and how soft you want it to be. You may need to steam it for about 5 more minutes.
Sprinkle with some salt before serving if you want to. Place the entire head of cauliflower on a platter or plate and serve alongside lemon wedges and butter, if desired.