Cook pasta until al dente in plenty salted water. While the pasta is cooking, heat a frying pan and melt the butter and add the smoked salmon. Fry over a medium heat for a few minutes then add the peas. Stir through then add the creme fraiche. Heat through quite gently until peas are cooked and salmon is warmed through. Check seasoning and add salt if required. Add plently black pepper and herbs if using.
When pasta is cooked, drain, reserving a little of the cooking water. Add salmon and sauce to pasta and mix well. Serve immediately.