"Takes some time, but worth the effort! Tastes like it comes from an upscale restaurant. More shrimp can be used, if desired, or a combination of any shellfish you like. It's even fabulous when made with poached salmon, cut into small pieces. If you opt for the salmon, use the poaching liquid in your sauce in place of the broth made with shrimp shells. In order to save time, shrimp and broth may be prepared a day ahead, and refrigerated until you're ready to finish the dish. If you like more bite, add a dusting of cayenne to the sauce. Pass more Parmesan for your guests to add as desired."
Put 2" water in a saucepan tall enough to set the colander on top (so that the bottom of the colander will be above the water.) Put pan on high heat.
When water is boiling vigorously, put the colander containing the shrimp on top.
Set a cover on the colander (it is not necessary that it closes tightly.)
Continue to boil until all the shrimp is pink and opaque.
Remove colander to the sink and cool the shrimp enough to peel.
Peel the shrimp, returning the shells to the steaming water. Set aside 4 of the shrimp for garnish. Reserve the rest, cutting in bite size pieces if the shrimp are very large.
Simmer the shrimp shells for 15-20 minutes. Watch to be sure pot doesn't run dry.
Strain the liquid, discarding the shells. If necessary, add enough water to make 1 cup.
Turn burner to medium. Melt the butter in a large pan, such as a skillet.
When melted and foaming, add the onion.
Boost heat to medium high. Stir the onion to carmelize, until it is evenly deep brown.
Add garlic and stir constantly for 1 minute. Add and saute mushrooms until tender, about 3 minutes.
Pour in the white wine, and increase heat to medium high. Simmer until the reduced by half.
Stir in the shrimp shell liquid. Stir in the mustard, 1 TB fresh basil (if using dried basil, add the entire tsp now,) lemon zest, lemon pepper, lemon juice, thyme and nutmeg, and cook gently until reduced and somewhat thickened.
Cook the fettuccine while you are reducing your sauce. Drain.
Stir sour cream and half the cheese into sauce. Taste for salt.
Toss the fettuccine together with the sauce and the shrimp in the skillet to heat through.
Center one of the reserved shrimp on top of each serving. Sprinkle with the remaining cheese and fresh basil.