Salmon fish cakes and spicy dip

For the salmon fishcakes:

400g floury potatoes, boiled and mashed

400g skinless salmon fillet, poached and flaked

2 spring onions, finely chopped

2 tsp capers

1 tbsp finely chopped dill

grated zest and juice of ½ lemon

50g butter

sea salt

black pepper

For the spicy dip:

100ml crème fraîche

1 tbsp peeled and grated Fresh horseradish root (jarred horseradish will do too)

grated zest and juice of ½ lemon

2 tsp finely chopped flat-leaf parsley

1 lemon, cut into wedges, plus a bunch of watercress (optional), to serve