Bring a large pot of salted water to a boil for the pasta.
Snap off the ends of the asparagus where they break naturally and cut into pieces about an inch long.
While the water is coming to a boil, melt the butter in a large heavy skillet. Add the shallots and asparagus and saute until shallots are soft. Stir in the cream and simmer about five minutes, until the cream has thickened somewhat.
Add the salmon to the cream and remove the skillet from the heat. Season with pepper and lemon juice.
When the pot of water is boiling, add the fettuccine, stir it once or twice, then cook until just before al dente. Drain.
If needed, warm the sauce and add fettuccine. Toss and add pepper or additional lemon juice. Sprinkle with dill and serve.