In a small saucepan on medium-low heat, melt butter. Bring to a boil and allow to brown for 1-2 minutes. Remove from heat, allow to cool for a few minutes.
In a large mixing bowl, add melted butter with powdered sugar, mix completely. Add flour and salt. Mix together (will be crumbly). Add in egg and butterscotch, mix until completely combined.
Line a 15x10x1 baking sheet with parchment paper. Place dough on baking sheet and press (with palms of hand) to about 1/4 inch thick. Shape into a rectangle (doesn't have to touch side of pan).
Bake in a 350 degree oven for 20-25 minutes, until lightly browned. Remove from oven and cool about 5 minutes. Using a sharp knife, make slices into cookies about 3-inch x 1-inch. Don't separate, allow to cool completely.
When cooled, separate cookie bars (using knife if necessary). Store in air tight container for one week. ENJOY!
Notes
The key to extra flavor is browning the butter before mixing it with the other ingredients. For best results, use powdered sugar, not granulated sugar.