Heat the oil in a large saucepan set over a medium heat. Add the bacon and sauté for 2 minutes, until lightly coloured. Stir in the onion, garlic, thyme and curry paste, then cover with a lid and sweat over a low heat for 5 minutes, stirring occasionally, until the onions are softened but not coloured.
Pour in the vegetable stock and butterbeans and bring to the boil, then add the cabbage and season to taste. Reduce the heat and simmer for 10 to 15 minutes, until the cabbage has softened.
Remove from the heat and blitz until smooth, then stir in the butter, if using. Check the seasoning and keep warm until needed. Serve piping hot and sprinkle with the chopped parsley, if using.