Preheat the oven to 350 degrees. Pick out 32 of the prettiest pecans (unbroken, etc) from the two cups and set aside. Lay the rest of the pecans in a single layer on a baking sheet and toast for 8-10 minutes until fragrant and browned. Remove from the oven and cool to room temperature.
Place the toasted pecans, brown sugar and confectioners sugar in the bowl of a food processor and pulse until the nuts are finely ground. Add the flour and salt and process to combine.
Add the butter and process until the mixture resembles wet sand and the mixture begins to ride up the sides of the bowl. Add the egg yolk and process until combined.
Cut a 15" long piece of plastic wrap and place on a work surface. Transfer half the dough to the plastic wrap and roll it into a log shape, about 2" in diameter. Roll up to seal in the plastic wrap. Repeat with the remaining dough. Place cookie dough logs in the refrigerator and chill for 2 hours until firm.
Adjust oven racks to upper middle and lower middle positions and heat oven to 325 degrees. Line two baking sheets with parchment paper.
Working with 1 dough log at a time, remove from plastic wrap and use a sharp chef's knife to cut the dough into 3/8" slices, rotating the log as you go so that the log doesn't become misshapen, from the weight of the knife. Place rounds 1" apart on the cookie sheet. Gently press a pecan half into the center of each cookie.
Bake cookies for 10-12 minutes -- one cookie sheet on the top rack and one on the bottom. Swap the cookie sheets around (bottom sheet to top rack and vice versa) and bake another 10-12 minutes until cookies are browned and crisp.
Cool cookies for 3 minutes on a baking sheet before transferring them to a wire rack to cool completely. Store in an airtight container.