Cook the pasta in a saucepan with salted boiling water according to the instructions on the package.
Meanwhile, slice the smoked salmon or chop it up into thin strips. Strip the leaves from the thyme sprigs.
Melt the butter in a large saucepan. Stir in the cream with about a quarter of the salmon and thyme leaves, then season with pepper. Heat gently for 3 to 4 minutes, stirring all the time. Do not allow to boil. Taste the sauce for seasoning.
Drain the pasta and toss it in the cream and salmon sauce. Divide among four warmed bowls and top with the remaining salmon and thyme leaves.