Melt the unsalted butter and let it cool for several minutes until warm rather than hot. This prevents the butter from making the dough excessively loose.

In a large bowl, whisk together the melted butter, brown sugar, granulated sugar, pumpkin puree, egg yolk, and vanilla extract until smooth and evenly combined. The mixture should look glossy and fairly thick.

In a separate bowl, whisk together the rolled oats, all-purpose flour, 1/2 teaspoon of the cinnamon, baking soda, salt, and nutmeg. Reserve the remaining 1/2 teaspoon cinnamon for the dough.

Add the dry ingredients to the pumpkin mixture: Stir with a rubber spatula just until no dry flour remains. Do not overmix. The dough should be thick and soft.

Fold in the 1 cup chocolate chips, reserving about 2 tablespoons for topping the cookies if desired. If the dough feels unusually loose, let it stand for 5 minutes; the oats will absorb some moisture.

Cover the bowl and refrigerate the dough for 30 minutes. Chilling makes the dough easier to scoop and helps limit spreading during baking.

Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.

Scoop the chilled dough into approximately 24 portions, using about 1 1/2 tablespoons of dough per cookie. Place them about 2 inches apart on the prepared baking sheets. Gently flatten each mound because these cookies do not spread dramatically.

Bake for 11 to 13 minutes, rotating the baking sheet halfway through if your oven browns unevenly. The edges should look set and lightly golden, while the centers should still look soft and slightly puffy.

If desired, gently press some of the reserved chocolate chips into the tops while the cookies are still warm. This gives the finished cookies a more chocolate-studded appearance.

Let the cookies cool on the baking sheets for 5 minutes, then transfer them to a wire rack. Allow them to cool completely before storing. The centers will firm while retaining a soft, chewy texture.