Make the dressing: Place the wine, mustard, sugar, tarragon and a little salt and pepper in a blender and blend until combined, then add the oil and blend again until amalgamated.
Wash and dry the rocket well and divide between 4 plates. Core the radicchio and then add to the rocket on the plates.
Add a quarter of the crab meat to each plate. Top with a quarter of the cherry tomatoes, artichokes and parsley.
Scatter over the zest of the lemon and the croutons, and drizzle with the dressing prior to serving.