Cook the tagliatelle in plenty of boiling salted water until al dente. While its cooking break the hot smoked salmon into flakes, discarding the skin.
Melt the butter in a frying pan and add the salmon. Cook for about a minute then add the vodka or wine. Continue to cook until most of the alcohol has evaporated.
Add the sour cream and heat through but dont allow it to boil. Add the dill and pepper- you should not need salt.
Drain the pasta and add it to the sauce in the pan. Toss everything together then divide among four warmed plates or bowls. Put a spoonful of keta on top of each serving.