Place the shredded cabbage in a colander over the sink and sprinkle with salt. Leave for 2-3 hours, then drain and wash away the salt. Pay dry with a clean tea towel.
Put the vinegar, wine, sugar, peppercorns and bay leaves into a big, wide saucepan and simmer until the liquid has reduced by about half. Set aside for 10 mins to infuse.
Strain through a fine sieve into a jug or bowl, and discard the peppercorns and bay leaves. Put the cabbage and mustard seeds into a big bowl, and then pour the strained liquid over. Transfer the cabbage and pickling liquid into sterilised jars and seal. Will last for a month in the fridge.