In a stand mixer, combine the butter, sugar, and salt. Beat on medium speed until smooth.

Add the egg yolks and vanilla and beat on low speed until blended.

Add the flour and mix until incorporated and a smooth dough forms.

Divide the dough into 4 equal portions. Roll each portion into a log 7 inches long and about 1 1/2 inches in diameter. Wrap the logs in plastic and refrigerate at least 2 hours.

Position a rack in the middle of the oven, and preheat to 350 degrees. Line baking sheets with parchment paper.

Using a sharp knife, cut each unwrapped log crosswise into slices 1/4 inch thick. Place the cookies 1 inch apart on the baking sheets.

Bake 12-15 minutes until the edges and bottoms are golden. Let cool on baking sheets for 5 minutes, then transfer to wire racks. Store in an airtight container at room temperature for up to 5 days.