Preheat the oven to 350F (180C or 160C on a fan-forced oven). Line baking sheets with parchment paper or silicone baking mats.
Whisk together the flour, baking soda, baking powder and salt in a medium bowl.
In a separate large bowl, beat together the butter, brown sugar and granulated sugar until creamy.
Beat in the egg and vanilla extract.
Starting with the mixer on a low speed, beat the flour mixture into the butter mixture until combined.
Stir in the chocolate chips and butterscotch chips. I typically reserve a few for adding to the tops of the cookies after they're baked.
For the dough into balls with about 1 - 1.5 tablespoons of dough each. Mine were slightly smaller than a golf ball. I like to use a cookie scoop for this.
Place dough balls 2 inches apart on the lined cookie sheets.
Bake 1 sheet at a time in the middle of the oven. Bake cookies for 9-11 minutes, or until the tops look just set. If they aren't flattening as much as you'd like, gently press the cookies down before baking.
Remove the cookies from the oven and cool the cookies on the cookie sheet for at least 10 minutes. Optionally, place a few extra chocolate chips and butterscotch chips on top of each cookie. Then transfer to a wire rack to continue cooling.