Remove the outer leaves of the cabbage and then cut in quarters. I only used 1/2 a cabbage for this but just double if you're cooking for many. Cut the core out of the cabbage at the base, then slice thinly.
Put the cabbage in a saucepan, add the butter, salt to taste and then add the 1/2 cup of water.
Bring to a simmer on the stove, stir, and let simmer until the water has mostly evaporated, at which point the cabbage should be tender.
If the rest of your dinner is ready, stir and simmer a few minutes just to evaporate the rest of the water.
If you're dinner's not quite ready, just set this aside and then bring back up to warm it through before serving.