Thinly slice the onion and shred or slice the cabbage.
Heat the oil in an oven-proof, heavy-based pan. Gently cook onion for about 10 minutes, until golden.
Add the sugar and stir for a minute or so, until it starts to caramelise. Add the vinegar, and stir. . Add the cabbage, the cider, cinnamon, and bay leaf, then season generously with salt and pepper.
Bring to a boil. Cover and let it cool for later cooking, or transfer immediately to a preheated oven.
Cook for about 30-40 minutes, until the cabbage is tender. Taste and adjust the seasoning.
Serve warm.