From the cookbook
Rich, savory, umami-packed egg yolks cured in a mixture of kosher salt and sugar, then gently dried until firm enough to grate. Use them like a hard cheese to add concentrated flavor and a delicate, golden finish to pasta, soups, salads, and vegetables.
Prepare the curing mixture
In a medium bowl, thoroughly whisk together the kosher salt and sugar until evenly combined. Spread approximately half of the mixture into an even layer in an 8 × 8-inch (20 × 20 cm) glass baking dish. Using the back of a tablespoon, create 4 evenly spaced depressions in the curing mixture, each large enough to hold an egg yolk.
Cure the egg yolks
Carefully place one egg yolk into each depression, taking care not to break the membranes. Gently sprinkle the remaining salt and sugar mixture over the yolks until completely covered. Tightly wrap the baking dish with plastic wrap and refrigerate for 4 days. During this time, the curing mixture draws moisture from the yolks, concentrating their flavor and creating a firmer texture.
Rinse and dry the yolks
After 4 days, preheat the oven to 150°F. Carefully remove the yolks from the curing mixture. Gently brush off as much excess salt and sugar as possible without damaging them. Rinse each yolk under cold running water until any remaining curing mixture has been removed. The yolks should now feel semi-firm and appear bright and translucent. Gently pat dry with paper towels.
Dry the cured yolks
Set a wire rack inside a rimmed baking sheet and generously coat the rack with nonstick vegetable oil spray to prevent sticking. Arrange the yolks on the rack, leaving space between each. Place in the preheated oven and dry for 1½–2 hours, or until the yolks are completely firm, opaque, and grateable, with a texture resembling a hard cheese such as Gruyère. Remove from the oven and allow to cool completely.
Serve
Using a fine grater or Microplane, grate the cured egg yolks directly over finished dishes, just as you would a hard cheese. They are especially suited to pasta, soups, salads, and other dishes that benefit from a concentrated savory finish.