Adjust oven rack to middle position. Preheat oven to 350 degrees.
Toast chopped pecans on a rimmed baking sheet in the preheated oven until fragrant, about 5-7 minutes; set aside and allow to cool.
To the bowl of a standup mixer, fitted with the paddle attachment, cream together butter, granulated sugar, and vanilla on medium speed until light and creamy, about 3 minutes.
With the mixer set on low, mix in flour, baking powder and salt just until combined, and the mixture looks like coarse salt. Mix in cooled pecans.
Remove dough to a work surface. Divide dough in half and roll each half into a 1 1/2 inch log. Wrap in plastic wrap and refrigerate for 60 minutes.
Line 2 baking sheets with parchment. Spread demerara or turbinado sugar out on another rimmed baking sheet.
Brush both of the cookie logs with the beaten yolks, allowing any excess to drip off. Roll each log in demerara or turbinado sugar, gently pressing to help it adhere.
Cut logs into 1/2 inch slices and place on prepared baking sheets 1 inch apart.
Bake one baking sheet at a time, on adjust center shelf, of preheated oven, for 18-20 minutes, or until cookie just edges begin to brown. Rotate sheets halfway through baking. Remove from baking sheets and place them on a wire rack to cool completely.