Preheat the oven to 350F.
Line a 7" x 11" baking pan with baking paper.
In a bowl, whisk together the flour, baking powder and salt.
In a large mixing bowl, cream the butter and sugar. Add the eggs, orange zest and vanilla extract. Mix until smooth.
Add the flour mixture in three batches, mixing after each addition.
Fold in the nuts, peanut butter morsels and dark chocolate morsels.
Pour into the prepared pan (the batter will be heavy), scraping the sides of the mixing bowl. Smoothen the top for even thickness.
Bake at 350F for 20 to 30 minutes.
Cool in the pan for 10 minutes. Transfer to a wire rack to cool some more.
Cut the butterscotch brownies into two-inch squares.