Toast the pecans in a dry skillet for 3-4 minutes until fragrant; cool and chop.
Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream the butter and brown sugar until light and fluffy.
Beat in the pumpkin puree, egg yolk, and vanilla until smooth.
Whisk together flour, cinnamon, nutmeg, baking soda, and salt in a separate bowl.
Fold the dry ingredients into the wet mixture until just combined.
Fold in the toasted pecans.
Scoop into balls and place 2 inches apart on the tray.
Bake for 11-13 minutes until edges are set.
Cool on the tray for 5 minutes before transferring to a wire rack.