In a heavy bottom pot over medium heat, melt the 2 sticks of butter with 1 cup of the butterscotch chips, stirring often.
In one bowl, add the flour, baking powder, and salt and whisk well.
In another bowl add the brown sugar.
When the butter and butterscotch have melted, pour over the brown sugar.
Whisk until well combined, 2 to 3 minutes.
Whisk in the eggs, egg yolk, and vanilla and whisk until incorporated.
Add the flour mixture and stir to combine.
Fold in the 1 cup butterscotch and 1 cup toasted pecans
Spread the mixture into a parchment paper lined 9 by 13 pan
Place in a 350° oven and bake for 25 minutes
Remove from the oven and let cool on a wire rack for 15 minutes
Remove from the pan and let cool for another 5 minutes