Cream together the brown sugar, butter, and egg.
Slowly fold in the pumpkin puree and spices, until the batter is completely combined.
Pour into a greased 9"x9" baking pan and bake at 350° for 15 minutes. The edges should be just beginning to brown and a knife poked in the middle should come out clean.
Cool in the baking pan.
To make the butterscotch sauce, microwave the butterscotch chips in a glass bowl for 1 minute, stirring once in the middle.
Add 1-2 tbsp milk to the melted chips and whisk together thoroughly until you have a deliciously gooey butterscotch sauce.
When the pumpkin bars are cooled completely, drizzle them with the butterscotch sauce and serve warmed.
