Mix the crème fraîche, mayonnaise, spring onions, dill, pickled gherkins and lemon juice in a bowl.
Lift the salmon off the skin, put it in the bowl and flake it into smaller pieces with a fork.
Fold everything together well and season to taste with salt and pepper.
Warm the sandwich rolls and fill them with crisp salad leaves, salmon salad and pickled red onions.*Top with finely chopped chives and plenty of fresh cress, if you like.