Fry the onion in butter for 2 mins, then add the bacon and cook for a few mins more until golden.
Stir in the cabbage and boiling water. Cook for 2 mins over a medium heat until wilted, then cover, turn the heat to low and cook for another 5 mins.
Uncover and stir well; the cabbage should have a little colour. If not, increase the heat and cook for a few moments more. Season to taste.