Preheat the oven to 160ºc fan/ 180ºC or 350ºF. Line a 9 inch (23cm) square tin with baking paper. *See notes
In a medium bowl add the sugar and eggs to a bowl and mix them well.
Melt the butter in a small saucepan or in the microwave, set aside to cool for a few minutes. Once cooled gently, pour the butter into the eggs and sugar.
Whisk them well.
Weigh the flour into the bowl and mix it into the eggs and sugar mixture. The mix will get really thick. Like really, really thick! *See notes
Once the batter is very well mixed, Pour everything into a square tin. Drop tablespoon-sized dollops of the spread over the blondies and swirl with a butter knife or a toothpick. Scatter the crumbled biscuit over the top and bake in a preheated oven for about 25 minutes.
When the blondies are done, they’ll be set when the pan is wiggled gently and the top will have a crust with a slight crackle look to it.
You can insert a knife into the blondies and if it comes out clean remove the blondies from the oven. Let them cool completely in the pan. Once cooled, cut into 9 equal squares.