Bring a large saucepan of water to the boil for the pasta. Peel and finely chop the onion and put aside.
Bring the wine or vermouth to the boil in a frying pan and boil for 1–2 minutes, until the liquid has reduced by half. Stir in the chopped onion and cook until softened, then reduce the heat to very low.
Add the pasta and some salt to the saucepan of boiling water. Return to the boil, then cook the fresh pasta for 4–5 minutes, or the dried pasta for 10–12 minutes, until al dente.
While the pasta is cooking, cut the smoked salmon into small strips. Add to the onion and wine mixture in the frying pan and heat through very gently.
Chop the dill. Rinse, dry and roughly chop the capers. Stir into the onion and salmon mixture in the frying pan.
As soon as the pasta is cooked, drain well and transfer to a large serving bowl.
Season the salmon mixture with black pepper to taste (it won't need any salt), then spoon over the pasta. Stir gently and serve.
If you cannot find fresh dill, use mint or flat-leaf parsley instead, while diced green olives or gherkins would make an agreeable substitute for the capers.
Serve the pasta as a starter, or turn it into a substantial main course by adding a mixed green side salad or a plate of thinly sliced tomatoes with fennel, black olives and lemon and olive oil dressing.