Bring a large pot of salted water to a boil. Add the fettuccine and cook as the label directs. Drain, reserving about 1/2 cup cooking water.
Meanwhile, melt the butter in a skillet over medium heat. Add the shallot and a pinch of salt and cook, stirring occasionally, until lightly golden, about 3 minutes. Whisk the cream, egg yolk and lemon zest in a bowl. Reduce the heat to low and add the cream mixture and cheese to the skillet. Cook, whisking, until slightly thickened, about 2 minutes. Season with salt and 2 to 3 teaspoons pepper.
Add the pasta to the skillet and toss, adding enough of the reserved cooking water to loosen the sauce. Divide among bowls and garnish with more pecorino. Serve with crusty bread, if desired.