Preheat oven to 350°F.
Spread chopped macadamia nuts in a single layer on a baking sheet. Bake for about 5 minutes, or until nuts just begin to turn golden (watch carefully, as nuts can go from toasted to scorched very quickly). Remove from heat and set aside.
Mix flour and baking powder together in a medium bowl. Set aside.
In a separate mixing bowl, combine brown sugar, miso, and melted butter. Stir until blended to a homogenous paste.
Beat eggs, then add to miso-sugar mixture along with vanilla extract and paste. Stir until fully combined.
Fold flour mixture into wet ingredients until just barely combined (careful not to over mix). Add nuts and butterscotch chips and fold into batter.
Line a 9" x 9" baking pan with parchment paper, leaving a little excess along the edges (to be used to pull the finished blondies from the pan). Pour the batter into the pan and spread with a rubber spatula.
Bake for 30-40 minutes at 350°F, or until the top is dry and golden and a toothpick inserted at the center comes out clean.
As soon as the pan is cool enough to handle, use the excess parchment paper to pull the blondies from the pan. Transfer to wire rack to cool completely.