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 the chopped milkybar as well as some milkybar chunks and a good handful of the milkybar buttons then stir in.
Pour the mixture into the tin, and spread. Add on the rest of the buttons and some more milkybar chunks to the top.
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.