Preheat the oven to 350°F. Line two large baking sheets with parchment paper or silicone baking mats and set aside.
Using mixer, beat the butter, brown sugar, and granulated sugar together for 1-3 minutes at medium speed or until well combined. Add the egg and vanilla extract and mix until fully combined.
Add the dry ingredients (flour, baking soda, salt and oats) and continue mixing on low speed until just combined, then mix in the butterscotch chips. Do not overmix cookies!
Using a medium scoop (1 & ½ tablespoons) or drop the dough by heaping tablespoonfuls onto the prepared baking sheets. Very gently press down with your hand to flatten slightly. Make sure to leave a little room between each ball of cookie dough as they will spread a little while they bake. For thicker cookies, scoop cookies and flash-freeze in fridge for 10-15 minutes before baking.
Bake for 10 to 12 minutes or until the edges of the cookies are lightly golden brown and the tops are set. Remove from the oven and cool on the baking sheets for 5 minutes, then transfer the cookies to a wire rack cool completely.
Best right out of oven, while they're still warm or dunked into some cold milk after they've cooled! YUM!
Store cookies in air-tight container as soon as they've cooled at room temperature.