Boil the fettuccine: Bring a large pot of well-salted water to a boil and cook the fettuccine according to the package directions until al dente. Scoop out 1 cup of the pasta water before draining, then set the pasta aside.

Season and sear the shrimp: Pat the shrimp completely dry with paper towels and toss with 1/2 teaspoon of the salt, 1/4 teaspoon of the pepper, and the garlic powder. Heat the olive oil in a large skillet over medium-high heat until it shimmers, then add the shrimp in a single layer. Cook 1 to 2 minutes per side, just until they turn pink, opaque all the way through, and curl into a loose C shape. Move them to a plate right away.

Melt the butter and garlic: Turn the heat down to medium-low and add the butter to the same skillet. Once it melts, stir in the minced garlic and cook about 1 minute, until it smells sweet and turns pale gold. Don't let it brown or the sauce turns bitter.

Simmer the cream: Pour in the heavy cream and bring it to a bare simmer, with just a few lazy bubbles around the edge. Let it cook 3 to 4 minutes, stirring now and then, until it thickens slightly and coats the back of a spoon.

Whisk in the parmesan: Reduce the heat to low. Add the parmesan a small handful at a time, whisking until each addition melts before adding more. Season with the remaining 1/2 teaspoon salt, remaining 1/4 teaspoon pepper, and the nutmeg if using.

Toss the pasta in the sauce: Add the drained fettuccine to the skillet and toss with tongs until every strand is coated. If the sauce is tighter than you want, loosen it with the reserved pasta water a few tablespoons at a time.

Add the shrimp back and serve: Fold the shrimp and any juices from the plate into the pasta and toss for about 30 seconds, just long enough to warm them through. Scatter the parsley over the top and serve with lemon wedges on the side.