Cook the fettucine in a pot of rapidly boiling salted water until al dente. Drain in a colander, reserving 1/4 cup of the pasta cooking liquid.

While the pasta is cooking, melt the butter in a medium saucepan over medium-high heat. Add shallots and saute until tender. Add heavy cream and bring to a boil. Cook until sauce has reduced slightly, about 5 minutes. Remove from the heat.

Return the pasta to the pot it was cooked in, set over medium-high heat along with the reserved cooking liquid. Add the butter-cream mixture and half of the Parmesan and toss to combine thoroughly. Season with salt and pepper, to taste. Sprinkle with remaining Parmesan and garnish with parsley, if desired.