Kids and adults will love these dense, pan-baked bars.
Heat oven to 350 degrees. Spread pecans on a baking pan. Bake until toasted, 5 to 10 minutes. Transfer pecans to a bowl to cool.
Butter a 9-inch-square cake pan, and set aside. In a medium bowl, whisk together flour, baking powder, and salt; set aside.
In the bowl of electric mixer, combine butter and sugars. Beat until light and fluffy, 2 to 3 minutes, scraping sides occasionally. Add eggs and vanilla; beat until well combined. Add flour mixture; beat just until combined. Fold in butterscotch chips and toasted pecans.
Using an offset spatula, spread batter into pan. Bake until surface is golden brown and a cake tester inserted into center comes out barely clean, 45 to 55 minutes. Transfer to a wire rack to cool. Cut into squares. Store in an airtight container up to 3 days.