After butter is melted and cooled slightly (5 minutes), add butter to large mixing bowl. Using electric mixer or hand mixer, cream the butter and light brown sugar together.
Add eggs, one at a time, and beat until incorporated. Mix in vanilla extract.
In a separate mixing bowl, combine together dry ingredients (baking powder, flour and salt).
Gradually add dry ingredients to butter/ sugar mixture and beat until mixed thoroughly. If using, stir in butterscotch chips.
Pour batter into parchment lined 9" baking pan. Bake for 35-40 minutes or until golden brown and edges are pulling away from the side of the pan. Allow to cool slightly before removing and slicing.
Store in an airtight container.
Notes
Be sure not to overcook your butterscotch brownies. They may appear slightly undone in the center, but will continue to bake while cooling.