Preheat the oven to 180C. Line a 25x25 cm square baking tray with baking paper. If you don’t have one, just use a bigger tray, pushing the dough to one side of the tray shaping it to a square. When baked and still hot just gently push one side of the dough with a spatula to make it straight.
Whisk together the flour, baking powder, baking soda, and salt in a bowl and set aside.
Whisk together the melted butter, sugars, vanilla and egg until combined. Add the dry ingredients and chocolate chunks and mix until just combined.
Drop the dough into the prepared tray and press firmly into an even layer about 1cm thick.
Bake for 16-18 minutes or until lightly golden brown on top.
Allow to cool completely in the tray before cutting into sticks perfect for dunking into milk!