For the cookie dough:
In the bowl of an electric mixer, combine the butter, seeds scraped from the vanilla bean pods, and vanilla sugar. Beat on medium-high speed until light and fluffy, about 2-3 minutes. Blend in the egg yolks one at a time, and vanilla extract. With the mixer on low speed, blend in the flour and salt until incorporated and a thick dough forms.
Gather the dough together and transfer to a piece of parchment paper. Form into a log about 1¾-inches in diameter. Roll the dough tightly up in the parchment paper, and twist the ends to seal. Transfer the dough to the freezer and chill until very firm, at least 2-3 hours.
When you are ready to bake the cookies, preheat the oven to 350˚ F. Line baking sheets with parchment paper or silicone baking mats. On a piece of wax or parchment paper, pour a line of turbinado sugar for coating the dough log. Remove the dough from the freezer, brush lightly with the egg wash, and roll in the turbinado sugar pressing gently to adhere. Transfer the dough to a cutting board and slice with a sharp knife into rounds just less than ½-inch thick. Place the dough rounds on the prepared baking sheets.
Bake, rotating the pans halfway through baking, until the edges are light golden and the cookies are just set, 14-15 minutes total. Let cool on the baking sheets briefly, then transfer to a wire rack to cool completely.
*Buying a vanilla bean or two in the grocery store is ridiculously expensive! I buy mine in bulk online, a much cheaper option. Plus then you always have vanilla beans on hand – a very good thing indeed!
** To make vanilla sugar, split a couple of vanilla beans and store in an airtight container with sugar for a while – at least a few days. That’s it! If you don’t have time to wait for vanilla sugar, no worries. These are just as delicious made with regular sugar.