Simmer the fresh salmon in the hot soup for 20 min on low heat, then cool. Cut the smoked salmon into pieces, put them with the butter in a large enough bowl and mash them with a fork to a cream. Add the olive oil and the cooked salmon, mash well with the fork and mix. Season the lot with lemon zest, pepper and maybe salt, put in the fridge.
The rillette can be prepared very well the day before. Remove from refrigerator about an hour before serving. Bring to the table with toasts.
These salmon rillettes have a very limited shelf life, 4 days, in the refrigerator.