Melt the butter in a medium saucepan over medium heat, swirling the pan often, for 5–8 minutes, until the butter smells nutty and has golden-brown flecks. Pour it, including the browned bits, into a large heatproof bowl and cool until warm but no longer hot, about 15–20 minutes.

In a medium bowl, whisk together the flour, baking soda, cinnamon, ginger, nutmeg, and salt.

Whisk the brown sugar and granulated sugar into the cooled butter until combined.

Whisk in the pumpkin puree, egg yolk, and vanilla until smooth.

Fold the flour mixture into the wet ingredients just until no dry streaks remain, then fold in the chocolate chips.

Cover the dough and refrigerate for at least 1 hour, or up to 24 hours.

Heat the oven to 350°F and line two large baking sheets with parchment paper.

Scoop the dough into 2-tablespoon portions, spacing them about 2 inches apart on the baking sheets; keep the second sheet refrigerated while the first bakes. Bake one sheet at a time for 11–13 minutes, until the edges are set and lightly browned and the centers still look slightly soft.

Cool the cookies on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.