Try this dressing with it, it really takes the bitterness off:
1/2 tsp of mustard
1 tsp of honey
1 tsp sugar
1/4 tsp of dried ginger
4tbsps of cider or wine vinegar (or ordinary vinigar mixed with wine)
shake of salt and pepper
1 tsp chopped basil, (or any herb available)
4 tbsps olive oil
Put all ingredients into a jar and shake well. Pour over any bitter salad leaves.
Hope that helps,
Ali