Our Classic Shortbread gets a familiar update with the addition of semisweet chocolate and walnuts.
Preheat oven to 300 degrees, with rack in upper third. Sift flour and salt into a bowl; set aside. Put butter into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until fluffy, 3 to 5 minutes, scraping down sides of bowl. Gradually add sugar; beat until pale and fluffy, about 2 minutes. Add vanilla.
Reduce speed to low. Add flour mixture all at once; mix until just combined. Stir in chocolate.
Halve dough. Transfer each half to a piece of parchment paper, and shape into a log. Roll in parchment to 2 inches in diameter, pressing a ruler along edge of parchment at each turn to narrow the log and force out air. Unwrap, and roll each log in walnuts. Wrap each in plastic, and refrigerate 1 hour.
Let stand at room temperature 10 minutes. Cut logs into 1/4-inch-thick slices. Space 1 inch apart on baking sheets lined with parchment. Bake until golden brown, about 30 minutes. Transfer cookies to a wire rack; let cool completely.