Into a medium bowl, sift flours and salt. Whisk in 1/2 cup chopped pecans, set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream butter and granulated sugar on medium-high speed until smooth and light, about one minute. Add the maple syrup, egg yolk, and extract; beat on medium speed until well combined. On low speed, gradually add flour mixture, beating until just combined. Dough should be smooth and pliable. Flatten into a disk. Wrap in plastic; chill until firm, 1 1/2 hours or overnight.
Preheat oven to 350 degrees. Line baking sheet with parchment paper.
On a lightly floured work surface, roll out dough to 1/4 inch thick. Cut out rounds using a two-inch cookie cutter; place one inch apart on prepared baking sheet. Brush tops with beaten egg; sprinkle centers with remaining 1/4 cup pecans. Sprinkle the entire surface with turbinado sugar.
Bake cookies, rotating baking sheet halfway through, until golden around the edges, 10 to 12 minutes. Transfer to a wire rack to cool.
Shortbread can be stored in airtight containers at room temperature up to four days.