Place the finely sliced red cabbage and onion in a bowl and sprinkle over the salt. Mix well. Loosely cover the bowl and leave the vegetables overnight.
The next day, rinse the cabbage and onion in a colander under running cold water to rinse off salt - make sure they are really well rinsed. Drain well and pat dry with kitchen paper or a clean tea towel.
Put the vinegar into a saucepan, add the spices, and bring to the boil. Remove the pan from the heat and stir in the granulated sugar. Leave to cool.
Pack the onions and cabbage into cold, sterilised jars, pressing down well. Pour over vinegar, making sure that each jar has some of the spices and that the vegetables are totally covered with vinegar.
Store in a cool, dark place for at least 2 weeks before using. It will keep for up to 3 months, stored in a cool, dark place. Keep jars in the fridge once opened. Perfect at Christmas with cold meats - enjoy!