Step 1: Brown the butter in a light-colored saucepan over medium heat, stirring constantly until it smells nutty and brown bits form. Transfer to a bowl and let cool for 15 minutes.
Step 2: Blot the pumpkin puree by spreading it on paper towels and pressing until the moisture is absorbed and the puree is thick and concentrated.
Step 3: Whisk the cooled brown butter with the brown sugar and granulated sugar until well combined.
Step 4: Add the egg yolk, blotted pumpkin, and vanilla extract, whisking until the mixture is smooth.
Step 5: In a separate bowl, whisk together the flour, pumpkin pie spice, baking soda, and salt.
Step 6: Gently fold the dry ingredients into the wet ingredients using a spatula until just combined.
Step 7: Scoop 2-tablespoon sized balls of dough onto a prepared baking sheet and bake at 350°F (175°C) for 10-12 minutes.
Step 8: Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.