Preheat oven to 375°F and line an 8x8 pan with parchment paper or non-stick foil.
Combine butter and sugar.
Stir in eggs and butterscotch sauce into the sugar mixture.
Add flour, baking soda, and salt, and mix until smooth.
Fold in the butterscotch chips.
Spread mixture into lined pan and bake 20-25 minutes, until a toothpick inserted into the center comes out with just a few crumbs.
Cool completely, then cut into squares.
Notes
For additional flavor, add white chocolate chips or toffee pieces, coconut, walnuts, or pecans. These mix-ins can also replace some or all of the butterscotch chips.This recipe can be doubled and baked in a 9x13 pan, but bake time may need to be adjusted slightly.