Preheat the oven to 350ºF. Line a 9×13” pan with parchment paper with an overhang on the sides to easily lift the blondies out of the pan after baking. Spray paper with nonstick cooking spray. Set aside.
In a large bowl, mix the butter and brown sugar until combined. Add in the eggs and vanilla and stir to mix. Add the flour, baking powder, soda, and salt and mix just until combined. Fold in chocolate chips and toffee pieces.
Spread the dough evenly into the prepared pan. Sprinkle with sea salt. Bake until the center is just set, about 30 to 40 minutes. Check early to be safe. Cool completely in the pan, then lift out by the paper and cut into squares.