Gather a large mixing bowl and combine old-fashioned oats, all-purpose flour, baking soda, cinnamon, and pumpkin pie spice.
In another bowl, whisk together melted butter, granulated sugar, brown sugar, egg yolk, vanilla extract, and pumpkin puree until smooth.
Gently pour the wet ingredients into the dry ingredients and stir until just combined.
Fold in 1.5 cups of butterscotch chips into the cookie dough.
Drop heaping spoonfuls of dough onto a parchment-lined baking sheet and flatten slightly.
Dot the remaining 0.5 cup of butterscotch chips on top of each cookie before baking.
Preheat oven to 350°F and bake cookies for 13-15 minutes until edges are golden brown.