In a medium saucepan, melt butter over medium-low heat. Remove from heat and stir in brown sugar and sugar. Stir for 2-3 minutes or until it becomes silky smooth and glossy.
Let cool for 5-10 minutes.
Stir in vanilla and egg yolk.
Stir in pumpkin.
Add flour, oats, baking soda, salt, cinnamon, and pumpkin pie spice.
Stir well to incorporate ingredients.
Let chill for 15 minutes. Preheat oven to 350 degrees.
Stir in chocolate chips.
Using a cookie scoop or two spoons, drop cookie dough on baking sheets.
Bake for 10-13 minutes or until lightly golden brown on edges.
Let set up for 5-10 minutes before removing from pan.