Line a 20cm/8 inch square pan with baking paper. See notes for tips on lining your pan
In a large bowl, whisk together the sugar, condensed milk and melted butter
Now add the eggs and vanilla and whisk until lovely and smooth
Add the flour, baking powder and salt and fold through with a silicone spatula, until almost combined (you don't want to overmix!)
Gently fold through the chopped chocolate until it is only just combined.
Spread mixture into pan and bake for 28 minutes.
Once baked, allow the Blondie to cool in the pan before removing it from pan and cutting into squares
Notes
For easy removal of cooled Blondies, I always line my pans with longer strips of baking paper. If the paper comes up over the edge of the pan, you will be able to easily grasp it, making it easier to pull the Blondies up and out of the pan.