Combine all-purpose flour, bread flour, salt, baking powder and baking soda in a bowl. Set aside.
In a mixing bowl, cream the butter and both sugars until light and fluffy, about two minutes.
Add in the eggs and the yolk, one at a time and beat well after each addition.
Mix in vanilla.
Add flour a little at a time, continuing to beat.
Stir in the butterscotch and chocolate chips.
Scoop the cookie dough, forming balls using a medium cookie scoop.
Wrap each dough ball in plastic wray and refrigerate for several hours or overnight.
When ready to bake, preheat oven to 350℉, unwrap dough balls and place on a parchment lined baking sheet about two inches apart. You may need two baking sheets.
Bake on the center rack of the oven for about 10-15 minutes, until the cookies are golden brown.
Cool for about 5 minutes on the baking sheet, then remove to a cooling rack to finish cooling.