Preheat the oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar for 1-2 minutes or until well combined.
With the mixer turned down to a low speed, mix in the egg yolks, vanilla extract, and salt until fully combined.
With the mixer continuing at low speed, slowly mix in the flour ½ cup at a time. The mixture will be crumbly at first, but it will come together as you continue mixing it.
Using a one-tablespoon cookie scoop or measuring tablespoon, measure out the cookie dough, roll it into balls, and roll each one in granulated sugar. (For a crunchier cookie, use a coarse sugar.) Then place cookie balls on prepared baking sheets.
Use your thumb (or the handle of a large wooden spoon) to press an indentation into each ball of cookie dough.
Bake cookies at 350°F (177°C) for 12-14 minutes or until the cookies are set and the bottoms are lightly browned. Remove from the oven and cool on the baking sheet for 10 minutes, then carefully transfer the cookies to a wire rack to cool completely.