Line a 9x13 inch baking dish with crisscrossed parchment paper and preheat the oven to 350°F conventional or 325°F convection (with fan). I sprayed and lined my pan with one piece of parchment paper then secured the sides with metal binder clips.
Melt the butter in a large heat-safe bowl in the microwave. You can also do this in a small pot on the stovetop. Then, add the butter to the large bowl. Whisk together to flour, baking powder, baking soda and salt in a medium bowl, if desired.
Add the dark and light brown sugar to the melted butter and whisk until completely combined.
Whisk in the eggs and the vanilla extract until no streaks of eggs remain.
Add the flour, baking powder, baking soda, and kosher salt. Stir until a cohesive batter forms. Fold in the butterscotch chips.
Pour the batter into the prepared pan and spread evenly with an off-set spatula.
Bake the blondies for 18-20 minutes until they are puffed completely. The edges will be golden brown, and the top will be completely matte. The blondie will start to deflate, and that is normal! Allow to cool at room temperature before slicing on a cutting board.
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Notes
Yield – 9x13 pan for thinner blondies or a 9x9 pan for thick blondies Presentation – They are perfect on their own, but you can serve them with caramel sauce or creme anglaise for an easy weeknight dessert. Flavor Tips – A high-quality vanilla extract will give the blondies a more well-rounded butterscotch flavor. Storage – Store your blondies in an airtight container at room temperature for three days or in the refrigerator for up to two weeks. Freeze well-wrapped for up to 3 months.