Heat 1 tablespoon of the oil in small saucepan over medium heat. Add the yellow onion and sweat it until it is soft but not browned, 2 to 3 minutes. Add all but ¼ cup of the corn kernels and the water. Simmer the corn gently until it is heated through and almost tender, 3 to 4 minutes. Taste the mixture, adding salt and pepper until it tastes good to you. Transfer the mixture to a blender and puree until smooth.

Heat a cast-iron skillet over high heat until it is smoking hot. Add the green onions and cook, turning once, until charred on two sides, about 1 minute per side. Remove the skillet from the heat, transfer the onions to a cutting board, and and chop finely.

Heat a large, deep skillet over medium heat and pour in the remaining 1 tablespoon oil. When the oil is hot, add the reserved ¼ cup (40 g) corn kernels and the chopped green onions and cook, stirring, for 1 minute, then stir in the corn crema. Keep warm over very low heat. Bring a large pot of salted water to a boil. Drop in the fettuccine and cover the pot to quickly return the water to a boil. Cook the pasta until tender but still a little chewy, 4 to 5 minutes. Using a spider strainer or tongs, drain the pasta by transferring it to the pan of sauce. Reserve the pasta water. Add about ½ cup of the pasta water and cook the mixture over medium-high heat, tossing and stirring vigorously until the sauce reduces slightly, becomes very creamy, and coats the pasta, about 2 minutes. Keep the pasta moving until pasta and sauce become one thing in the pan, adding a little more pasta water if necessary to create a creamy sauce. Taste it, adding salt and pepper until it tastes good to you. Dish out the pasta onto warmed plates and grate the ricotta salata over the top.

From Mastering Pasta

by Marc Vetri and David Joachim (Ten Speed Press, 2015)