Pre-heat the oven to 350 and get our your baking dish: 8x8, 7½x10½ or 9x13 - set aside
Take 1 stick of cold butter straight from the refrigerator and heat it in the microwave for about 20 seconds, up to 30 until butter is softened but hasn't melted. A few melty spots are ok but you want it mostly solid
Add slightly warmed butter and 6oz of room temperature butter into bowl of stand mixer. Add in sugars and molasses - mix on medium speed for about 6 minutes or until mixture is fluffy and has lightened in color
Add in yolk and whole egg and vanilla and mix on medium speed until voluminous, about 3 minutes.
Add in 1 cup of flour, slowly, while mixer is mixing on lowest speed. Add in baking powder, soda, and salt. Then add in remaining flour the same way, slowly while mixer is running on low speed.
Pour in chocolate chips and butterscotch chips and mix for another 30 seconds - 1 minute more until the dough is well-combined and the flour has been fully incorporated into the dough.
Turn the dough over into your 7½x10½ pan and bake for 25 minuets or until top is set and a toothpick inserted into the middle of the bars comes out clean. See blog posts for varied times based on your pan size.
Let cool for 15 minutes, cut and serve with ice cream! Or eat as is :)