Preheat the oven to 350 degrees F. Grease a 9-inch baking pan with butter and line with parchment paper.
In a large bowl, whisk the butter, both sugars, eggs and vanilla extract. In a medium bowl, combine the flour, baking powder and salt. Stir the dry ingredients into the wet ingredients until just combined. Fold 2 cups candy into the batter and spread in an even layer into the prepared baking pan. Press the remaining candy on top.
Bake for 35-40 minutes until the blondies are golden brown. Cool completely before cutting into 16 squares.