Preheat oven to 375° Fahrenheit. Line a 9x13-inch baking pan with parchment paper. Spray the sides of the pan with nonstick cooking spray. Set pan aside.
Cream the brown sugar and butter together in the bowl of an electric mixer using the whisk attachment.
Add eggs and vanilla and beat until smooth.
Combine flour, baking powder and salt. Add the dry mixture to the butter mixture.
Fold in white baking chips and toffee chips.
Pour blondie batter into prepared pan. Bake for 30 to 40 minutes or until the center is set and a toothpick inserted comes out clean.
Allow blondies to cool completely before cutting and serving.