In a large bowl, combine mixed salad leaves, carrots, cucumber, cherry tomatoes and onions. Top with eggs.
To made the salad cream. Add the egg yolks, mustard, the juice of half a lemon, sugar and cider vinegar to the blender. Pulse to make a smooth liquid. Pour in the cream and blend slowly to mix. Mix in some chopped fresh tarragon. Add salt and crushed black pepper to taste. Taste and adjust seasoning. Pour the salad cream into a sterilised jar and place into the fridge until ready to use.
Drizzle the salad cream over the salad just before dressing.