Preheat your oven to 180C/160C Fan and line a 9x9" square tin with parchment paper. Melt the butter and white chocolate together.
In a large bowl, add the melted butter white chocolate mix and sugars and beat until smooth. Add in the eggs and vanilla and beat again until smooth.
Add in the flour and baking powder and beat till a thick blondie mixture is made. Add in most of the chocolate chips, kinder chocolate, and kinder bueno, and fold through.
Pour the mixture into the tin, and spread. Dollop on the nutella and lightly swirl through the blondie mixture. Add on the rest of the chocolate chips, kinder chocolate/bueno pieces!
Bake the Blondies in the oven for 25-30 minutes, or until there is a slight wobble in the middle. Leave to cool in the tin, or on a wire rack.