Preheat oven to 350°F (175°C) and grease a 9x13 inch baking pan.

In a large mixing bowl, beat together unsalted butter, light brown sugar, and granulated sugar until light and fluffy.

Add eggs one at a time, beating well after each addition, then stir in vanilla extract.

In a separate bowl, whisk together all-purpose flour, baking soda, and salt.

Slowly fold the dry ingredients into the wet mixture until just combined.

Fold in the butterscotch chips until evenly distributed.

Pour the batter into the prepared pan and bake for 20-25 minutes.

Cool completely in the pan before lifting out and cutting into squares.