Preheat your oven to 180C/160C Fan and line a 9x9" square tin with parchment paper. Melt the butter and 100g 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 half of white toblerone and half of milk toblerone bar, white chocolate and milk chocolate chunks and fold through.
Pour the mixture into the tin, and spread. Add on the rest of the chocolate chips and 4 toblerone triangles on 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.