Have on hand a piece of parchment paper (cut to about the size of a baking sheet) and a bench knife.

In a medium bowl, mix the sugar, lemon zest, and vanilla beans (if using) together until well combined. Add the mixture to the bowl of a stand mixer fitted with the paddle attachment, along with the butter, and cream until the mixture is light and fluffy, 4-5 minutes.

Add the egg yolks and mix well to combine. Scrape the bowl well, then add the flour and salt and mix until a smooth dough forms. 

Form the dough into a rough log and place it on one of the longer edges if the parchment paper. Using the edge of the parchment paper, wrap the log up, holding the edge of the paper in your hand once the log is fully encased. Place the bench knife at the edge of the paper’s seam to apply pressure to the dough, allowing it to form a longer, skinnier log while wrapped inside the paper. Once you’ve achieved a log about 1 ½ inches in diameter, transfer to the freezer and chill until firm, 20-30 minutes.

Preheat the oven to 350°F with the racks in the upper and lower thirds of the oven.

Use a sharp knife to cut the cookie into ¼ inch thick slices, then transfer them to the prepared baking sheets, leaving about ½ inch between each cookie (they won’t spread much).

Bake the cookies, rotating the sheets halfway through baking, until they are golden on the the outside edge, 13-15 minutes. Cool completely before serving.