Preheat the oven to 350° F (180° C).
In a stand mixer or with an electric hand mixer, cream together the butter, brown sugar and sugar until light in color and fluffy in texture. This will take approximately 2-3 minutes.
Scrape the sides of the bowl to incorporate all ingredients and add in the egg and canola oil. Mix until well combined.
Next, add in the flour, rolled oats, cornstarch, cinnamon, baking soda and salt. Mix until the dough forms.
Once the dough has formed, add in the butterscotch chips and mix until they’re evenly distributed.
Portion the dough out - for small cookies, use 1 1/2 tbsp of dough for each cookie. For larger cookies use 3 tbsp of dough. Roll the dough into balls.
Place the dough balls on a cookie sheet lined with silicone or parchment paper.
Bake at 350° F (180° C) for 8-10 minutes (small cookies) or 10-12 minutes (larger cookies). You’ll know the cookies are done when the cookies spread slightly and no longer look wet and glossy on top.
Allow the cookies to cool on the pan for 5-10 minutes before serving.
Enjoy!