Shortbread doesn't like to brag. It doesn't mind that some cookies are packed with chocolate chunks and colorful confetti. It doesn't need to prove its worth with cream filling or extra glaze. Shortbread can just sit back content in the knowledge that it's the most buttery, melt-in-your-mouth, make-you-weak-in-the-knees cookie on the block. Shortbread has nothing to prove. It doesn't necessarily need a lift from brown sugar and black sesame seeds, but it doesn't mind the classy company. —Joy Wilson
about 50 cookies
(2 sticks) unsalted butter, at room temperature
Put racks in the center and upper third of the oven and preheat the oven to 325° F. Line 2 baking sheets with parchment paper.
In the bowl of an electric mixer fitted with the paddle attachment, beat together the butter and sugar until light and fluffy, 3 to 4 minutes.
In a small bowl, whisk together the flour, cornstarch, salt, and sesame seeds. Add the flour mixture to the butter mixture, 1 cup at a time, beating after each addition, until it is all incorporated. The mixture will be thick and crumbly. Transfer it to a counter and knead it into a smooth dough. Wrap the dough in plastic wrap and refrigerate for 20 minutes.
Transfer the chilled dough to a lightly floured counter and roll it into an 1/2 inch-thick triangle. Cut it into 2-inch squares, and cut each square into triangles. Transfer to the prepared baking sheets.
Bake until just lightly golden brown around the edges, 20 to 22 minutes. Remove from the oven and let cool. The cookies will keep in an airtight container at room temperature for up to 7 days.