A very simple method of preparing Swiss chard and/or beetroot leaves (they are very similar, you can mix them) is:

1. Fry a chopped onion gently in butter with a little salt in a saucepan or deep frying pan.
2. Wash the leaves carefully then chop them up.
3. Add to the onion and cook gently until soft, stirring from time to time.

Nice as a side vegetable, or served with eggs.