Cook 1 minced shallot in a skillet with 1 tablespoon butter over medium heat until golden, 3 minutes. Whisk 1 1/4 cups heavy cream, 1 egg yolk and 2 teaspoons grated lemon zest in a bowl; reduce the heat to low and whisk into the skillet along with 1/3 cup grated pecorino. Whisk until slightly thickened, 2 minutes. Season with salt and plenty of pepper. Toss with 12 ounces cooked fettuccine and some pasta-cooking water. Top with more pecorino.