Watercress sauce is a classic accompaniment to salmon. The green-flecked, sharp and peppery sauce acts as the perfect complement, aesthetically and culinarily, to the fatty creaminess of the pink-fleshed fish. This sauce is fairly light, very sharp, and easy to make. I like it served hot with poached salmon fillets, but please do not feel constrained by my salmon cooking preferences.
Ingrediments enough for at least six servings
Method
Begin by melting the butter with the oil in a sauce pan and frying off the shallot until it is tender but not coloured. Then add the wine and allow it to bubble and reduce slightly. Add the watercress, which you might need to do in two stages owing to bulk, and let it wilt. When the watercress has succumbed, tip in the crème fraîche and let it bubble gently (don't boil it) and thicken slightly. Season with salt and pepper, going gently with the pepper because the watercress' inherent spiciness.
If your saucepan is suitable, blitz it in there using a hand blender. Otherwise transfer it to a jug or use a food processor or blender. You can serve it immediately, or let it rest and then heat it through again just before serving at a later time.
I use crème fraîche because I prefer the sharper flavour and lighter consistency it gives this sauce. There's nothing to stop you from substituting cream if you want something more unctuous and decadent. I'd add a squeeze of lemon juice too, though, to help with the flavour.