Preheat your oven to 160C Fan / 180C and prepare a 9×9 inch square tin with non stick baking paper – it needs to be fairly deep.
In a large bowl mix together your melted (and cooled) butter with your caster sugar and light brown sugar. Mix until properly combined and you no longer see the yellow of the liquid butter.
Add in your eggs and vanilla extract, mix until combined.
Add in your gluten free flour, cornflour and xanthan gum. Briefly mix until just combined and the mixture is smooth without any visible flour or lumps.
Fold in your white chocolate chips.
Spoon / pour the mixture into your tin, spreading the mixture to the edges so it’s nice and evenly flat. Sprinkle a few extra white chocolate chips on top.
Bake in the oven for around 30 minutes. The very centre might still seem a little wobbly but the outer edges should be fairly cooked through. If you cook it for not long enough, it will still be liquid, if you cook it for too long it will be like a cake, not a blondie!
Remove from the oven and allow the blondie to completely cool in the tin.
