How to Make It
In a large skillet, heat the olive oil. Add the pancetta and cook over moderate heat until crisp, about 7 minutes. Drain the pancetta in a strainer over a bowl; reserve 2 tablespoons of the fat.
Add the cream to the skillet and bring to a simmer over moderate heat. Grind black pepper into the cream, then add in the Parmesan and the 1/2 cup of pecorino, stirring until the cheese has blended into the cream, about 2 minutes. Scrape the mixture into a bowl and let cool. Whisk in the egg yolk, pancetta and the reserved pancetta fat and refrigerate.
Bring 4 quarts of water to a boil; add the salt. Spread the semolina on a large, rimmed baking sheet. Put 1 cup of cold water in a bowl. Dip your fingertips in the water and scatter drops all over the surface of the semolina. Keep scattering until the entire surface is covered with drops. With a rubber spatula, turn the moistened semolina over on itself, tossing to form small lumps. Shake the pan to spread the loose semolina in an even layer. Repeat with more water until just about all of the semolina has been formed into irregular lumps about the size of small peas. Shake the frascatelli in a colander to remove any loose semolina.
Pour the frascatelli into the boiling water and cook, stirring a few times, until al dente, about 4 minutes.
Meanwhile, in a large, deep skillet, gently reheat the sauce over moderately low heat, stirring constantly. Drain the frascatelli, add it to the sauce and bring to a simmer, stirring. Transfer the frascatelli to shallow bowls and serve, passing grated pecorino at the table.