Preheat oven to 180°C, bake. Grease a 22 x 22cm tin and line with baking paper
Melt butter in medium saucepan on low heat. When no lumps, add sugar and whisk until combined
Remove from heat, allow to cool slightly then add eggs one-by-one, whisking well in between each
Whisk in vanilla
Sift in flour, cocoa, baking soda, and add chocolate chunks
Gently fold with a wooden spoon until only just combined - don't overmix or brownies will be tough
Bake for 20 minutes or until the skewer is clean
Cool in tin before slicing, dust with icing sugar