Preheat oven to 350°F (175 degrees C). Spray a 9x13-inch baking dish with baking spray.
In a large mixing bowl, stir together flour, oats, baking powder, baking soda, and salt. Set aside.
To the bowl of a stand mixer with the paddle attachment, add butter and brown sugar. Beat on low speed until smooth.
Add eggs, molasses, and vanilla. Mix until all ingredients are fully incorporated, stopping to scrape down the sides of the bowl as needed.
With the mixer still on low speed, slowly add the dry ingredients until fully incorporated.
Add 1 ½ cups of butterscotch chips and mix until just combined.
Press the dough into the prepared baking dish. Sprinkle the top with the remaining ½ cup of butterscotch chips.
Bake for 25-30 minutes, or until golden and an inserted toothpick comes out with a few crumbs, but not wet batter. Allow bars to cool in the pan.
Drizzle with butterscotch sauce. Cut and serve.