These German sable cookies are a delicous treat courtesy of Johnny Iuzzini.
In the bowl of an electric mixer fitted with the paddle attachment, mix together butter, sugar, and 1/2 teaspoon salt until creamy. Using a rubber spatula, work hard-boiled egg yolks through a fine sieve and add to the mixer; mix until well incorporated. Add flour and vanilla and continue mixing until well combined, 2 to 3 minutes, scraping down the sides of the bowl as needed.
Wrap dough with plastic wrap and refrigerate until chilled.
On a lightly floured surface, roll out dough 1/2 inch thick. Transfer to a baking sheet and refrigerate until chilled. Cut dough into 3-by-1/4-inch-wide strips and transfer to a baking sheet lined with parchment paper or a nonstick baking mat. In a small bowl, mix together egg, yolk, and pinch of salt. Brush each strip with egg mixture, and garnish if desired. Freeze until firm, about 15 minutes.
Preheat oven to 375 degrees. Transfer baking sheet to oven and bake until lightly golden, about 12 minutes.