Make sure the salmon is well chilled, then cut it into 5mm cubes using a very sharp knife. Transfer them to a large bowl.
Finely chop the spring onion, capers and gherkins, then add them to the bowl with the salmon.
Add the chopped fresh dill, the juice of half a lemon, extra-virgin olive oil and Dijon mustard. Gently fold everything together so you don’t break up the salmon.
Taste and season with fine salt and freshly ground black pepper as needed.
Cover the bowl with cling film and chill in the fridge for 15-20 minutes to allow the flavours to meld.
To serve, if desired, use a ring mould and serve the salmon tartare with thin toast, blinis or avocado slices.