01 - In a medium saucepan over medium heat, melt unsalted butter, stirring often until it foams, turns golden, and gives a nutty aroma (about 5 to 7 minutes). Transfer to a mixing bowl and let cool for 10 minutes.
02 - Preheat oven to 350°F (175°C) and line two baking sheets with parchment paper.
03 - In a large bowl, whisk together all-purpose flour, baking soda, baking powder, salt, ground cinnamon, ground ginger, ground nutmeg, and ground cloves until thoroughly mixed.
04 - Add light brown sugar and granulated sugar to cooled brown butter. Whisk briskly until homogenous.
05 - Add pumpkin purée, egg yolk, and vanilla extract to the butter-sugar mixture. Stir until the mixture is smooth.
06 - Gradually fold the dry ingredients into the wet mixture until just incorporated, avoiding overmixing.
07 - If desired, gently mix in chocolate chips and/or chopped toasted pecans or walnuts.
08 - Using a cookie scoop or spoon, portion approximately 2 tablespoons of dough per cookie onto prepared baking sheets, spacing them 2 inches apart.
09 - Bake for 10 to 12 minutes until edges are set and centers appear just underdone.
10 - Let cookies rest on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.