1. Whisk the flour and salt together in a medium bowl. In a bowl of a standing mixer, beat the butter and sugars together until light and fluffy, 3 to 6 minutes. Beat in the egg yolks and vanilla until combined, about 30 seconds, scraping down the bowl and beaters as needed. Reduce the mixer speed to low and slowly add the flour mixture until combined, about 30 seconds.
2. Transfer the dough to a clean counter and divide it into 2 equal pieces. Roll each piece of dough into a 6-inch log, about 2 inches thick. Wrap the dough tightly in plastic wrap and refrigerate until firm, about 2 hours.
3. Preheat the oven to 325 degrees. Line 2 large baking sheets with parchment paper.
4. Working with one log of dough at a time, slice the dough into ¼-inch-thick cookies. Lay the cookies on the prepared baking sheets, spaced about ¾ inch apart. Bake the cookies until the edges begin to brown, 12 to 15 minutes, switching and rotating the baking sheets halfway through baking.
5. Let the cookies cool on the baking sheets for 3 minutes, then transfer to a wire rack to cool completely before serving.

Chocolate Icebox Cookies

Substitute ¼ cup Dutch-processed cocoa powder for ¼ cup of the flour. Add 2 ounces melted and cooled semisweet chocolate to the dough with the egg yolks and vanilla.

Pinwheel Icebox Cookies

Make the dough for both Vanilla Icebox Cookies and Chocolate Icebox Cookies just through step 1 (don’t roll the dough into logs). 

1. Roll the vanilla and chocolate doughs each into a 12-inch square between 2 pieces of wax paper. Remove the top sheet of wax paper from both the vanilla and chocolate doughs and flip the chocolate dough so that it is on top of the vanilla dough. Gently roll over the top with a rolling pin to make the doughs adhere.
2. Trim the dough to a tidy 12-inch square with a knife. Roll the dough into a tight 12-inch-long log. If you have trouble rolling the log, lift up the wax paper and use it for leverage.
3. Wrap the dough tightly in plastic wrap and refrigerate until firm, about 2 hours.
4. Slice each log into ¼-inch-thick cookies and bake as directed for the Vanilla Icebox Cookies above.

Checkerboard Icebox Cookies

Make the dough for both Vanilla Icebox Cookies and Chocolate Icebox Cookies just through step 1 (don’t roll the dough into logs).  

1. Divide the vanilla and chocolate doughs each into 2 pieces. Roll each piece into a 6-inch log, then press each log into a 1½-inch-thick square shape. Quarter the squared-off logs lengthwise with a chef’s knife.
2. Layer 2 strips of vanilla and 2 strips of chocolate dough into a checkerboard pattern and squeeze together gently to adhere. Repeat with the remaining strips to make four 6-inch checkerboard logs. Wrap the dough tightly in plastic wrap and refrigerate until firm, about 2 hours.
3. Slice each log into ¼-inch-thick cookies and bake as directed for the Vanilla Icebox Cookies as above.