Bring a large pot of well-salted water to a boil and cook the pasta for 2 minutes longer than the package instructions indicate so it holds up in the salad.
Drain the pasta in a colander and rinse briefly under cold running water to stop cooking and cool the pasta; drain well.
In a small bowl, whisk together the mayonnaise and sour cream; season with salt and pepper to taste.
Place the cooled pasta in a large bowl and pour the dressing over it; stir gently to coat evenly.
Add the finely chopped celery, gherkins, dill and chives to the dressed pasta and fold together until combined.
Tear or chop the smoked salmon into bite-sized pieces, add to the pasta, and stir gently to combine.
Grate about 1 tablespoon of lemon zest over the salad, adjust seasoning with salt and pepper, garnish with extra dill and chives, and serve or refrigerate for up to 24 hours.