In a large mixing bowl or stand mixer, add the butter and beat on medium-high speed until smooth, about one minute.
Add the brown sugar and beat with the butter until creamy, about two minutes.
Add the egg and maple extract. Beat on high speed for about one minute. Stop the mixer and scrape the sides of the bowl as needed.
Add the flour, cinnamon, and salt and mix on low speed until everything is combined.
Add the chopped walnuts and mix on low speed until the walnuts are evenly distributed throughout the dough. The dough will be thick and sticky.
Turn the dough out onto a floured cutting board and divide into two equal pieces. Shape each piece into a log about two inches in diameter. Wrap tightly in plastic wrap and place in the refrigerator for at least four hours (up to five days).
When ready to bake, heat your oven to 350 degrees F. Remove your cookie dough from the refrigerator and slice each log into about 16 cookies (each cookie will be about 1/2-inch thick).
Place the sliced cookies two inches apart on baking sheets lined with parchment paper or silicone mats.
Bake for 12-14 minutes, until the bottom edges start to brown. Allow to cool slightly on baking sheets before transferring to wire racks to cool completely.