Preheat oven to 350 degrees F. and line a large baking sheet with parchment paper.
Place butter and sugars into a large mixing bowl, stirring well to combine. Add egg and vanilla stirring to combine. Slowly add flour, oats, baking soda, salt and butterfinger, stirring until dough forms.
Scoop onto baking sheet 1 inch apart. Bake for 11-13 minutes until baked through. Let cool completely before transferring. Serve room temperature.