Preheat your oven to 180C/160C Fan and line a 9x9" square tin with parchment paper.
In a large bowl, add the melted butter, white granulated sugar and light brown soft sugar and beat until smooth.
Add in the eggs and vanilla extract and beat again until smooth.
Add in the flour and custard powder and beat until a thick blondie mixture is made - it really doesn't take long to create this mixture!
Add in the custard creams and white chocolate chips and fold together.
Bake the custard cream blondies in the oven for 25-30 minutes, or until there is a slight wobble in the middle. (See notes below)
Leave to cool in the tin, or on a wire rack.
As an optional extra, you can 'set' your blondies in the fridge for an hour or so to help with the texture! ENJOY!
The bake time can vary - please make sure your oven is on the correct setting, and check from 22+minutes and onwards till they are baked! These took 25 minutes in my fan oven.
If they turn out cakey, they are over baked - that's all! Bake for a little less time next time.
One top tip is if they've been in for the 25-30 minutes, and you're still not sure, let them cool outside of the oven fully and then put them in the fridge for at least an hour to 'set'. It can firm them right up! Over night in the fridge is best.