In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter, brown sugar and granulated sugar on medium speed until smooth and creamy, about 2 minutes. Scrape down the bowl.
Mix in the vanilla. Add the flour, cinnamon and salt, then mix on low just until no dry flour remains. Mix in the chopped pecans. Do not continue beating once the dough comes together.
Press the dough together and shape it into an 8-inch log about 2 inches in diameter. Wrap it tightly in plastic wrap and roll it gently on the counter to smooth the sides.
Refrigerate the dough for at least 4 hours, or until firm. The wrapped log can be refrigerated for up to 3 days.
Preheat the oven to 350 degrees F (175 degrees C). Line two baking sheets with parchment paper.
Combine the turbinado sugar and 1/4 cup chopped pecans in a shallow dish. Unwrap the chilled log and roll it in the coating, pressing gently to help it stick.
Cut the log in half, then cut each half into eight equal slices for 16 cookies. Place the slices cut-side down on the prepared baking sheets, leaving about 2 inches between them.
Bake for 12 to 14 minutes, until the centers are set and the bottom edges are pale golden. Avoid waiting for the tops to brown.
Cool on the baking sheets for 5 minutes, then transfer the cookies to a wire rack to cool completely.
Notes
Measure the flour by weight if possible. Too much flour is the most common reason shortbread becomes dry and difficult to slice.
If the coating does not stick, let the cold log rest for 5 minutes and press the coating on. Brush it with a very small amount of water only if needed.
Espresso variation: Omit the cinnamon and add 2 teaspoons instant espresso powder with the flour.
Store cooled cookies in an airtight container for up to 3 days, or freeze them for up to 2 months.