Shred the cabbage finely, discarding the tough core, and wash thoroughly.
Melt the butter in a heavy casserole and add the caraway seeds and the cabbage. Cook very gently, covered with a lid, over a low heat until the cabbage is soft. This will take up to an hour.
Pour off any excess butter then season with salt. Stir in the cream and mustard. Bring slowly to the boil then add a squeeze of lemon juice and serve.