Pickled red onion & radish

Slice 1 large red onion into thin rings and 12 small radishes into thin slices. Stir in 1 tbsp salt and 1 tbsp golden caster sugar and leave for 20 mins. Warm 100ml cider vinegar and 50ml water in a small saucepan, then pour over the vegetables. Stir to dissolve the sugar and salt, then leave to cool.