Preheat oven to 180°C/ 160°C fan assisted. Grease and line a 9"x9" (22cm x 22cm) square tin using the sling method (see image below with blondie batter in the tin).

Melt the butter in a heat-proof bowl in the microwave. Add in the sugars, and whisk together. Then pop the butter-sugar mixture back into the microwave for 30 seconds, whisk again and repeat 2 times. When you are done the sugar will have dissolved into the butter, and the mixture will have thickened. Allow to butter mixture to cool a bit. Add in the spices and vanilla extract. Whisk through. Add the eggs and whisk vigorously for at least a minute.

Add the flour, salt and baking powder and stir through until just mixed. Add the walnuts and stir through. Pour into the prepared tin, give a few good bangs on the kitchen counter to remove air bubbles and bake for 25 to 30 minutes or until the chai spiced blondie bar has just set.

Allow the blondie to cool in the tin for 30 minutes before lifting out using the baking paper slings and cool completely on a wired rack. Slice into 16 to 25 pieces, serve and enjoy!