Slice the courgettes, not too thinly. Sprinkle with salt and leave in a colander for 15 minutes to draw out the water. Rinse in cold water, drain well and dry carefully in a clean cloth or on kitchen paper.
Fry the courgettes, in batches if necessary, in the oil, and drain on kitchen paper. Arrange the slices neatly on a serving dish and keep hot.
Shred the sorrel and sprinkle with a little salt. Leave for 10–15 minutes. Heat a tablespoon or so of oil and throw in the sorrel. Cook, stirring, for 4–5 minutes until the sorrel has collapsed and the water has been driven off. Spoon the sorrel over the courgettes and serve hot or cold.
Jeannette adds that should sorrel be unavailable you could prepare courgettes au vinaigre (courgettes with vinegar), as a pleasing alternative. Heat a little olive oil, stir in a chopped clove of garlic and some coarsely chopped parsley. Cook until soft but not coloured. Carefully add a little wine vinegar, taking care that it does not spit. Remove from the heat, and pour over the courgettes and serve hot or cold.