In a medium sized bowl, whisk together the brown sugar, sweetener/sugar and butter/oil until mixture is light and fluffy. Whisk in the egg and maple syrup.
In a separate large bowl, whisk the flour, baking powder and salt. Pour the liquid mixture into the dry ingredients and fold gently with a wooden spoon until combined (Do not over beat batter, or blondies will be tough)
Pour batter into prepared baking tray and smooth to even out the top. The batter should be on the thick side.
Bake until golden, about 30 - 40 minutes, or still soft on the inside but just firm to the touch. (The centre should be just cooked through to create the perfect fudge-like blondie)
Cool completely in the pan before removing and gently cutting into 16 bars.