Grilled Salmon with Watercress Cream Sauce

A nice variation on the salmon-with-watercress-theme (see my Watercress Crème Fraîche Tart for more of the kind), and a welcome change to our usual uninspired salmon steak with leak and potatoes (though delicious too). It was somewhat difficult to get the seasoning of the sauce right. We doubled the amount of sauce to use it with pasta.

Edited to add: I have a new 'grilled salmon steak with veggies and potatoes'-theme favourite: Grilled Salmon with Lemon Courgettes!