Cream together the butter and sugars until light and fluffy
Stir in the milk, vanilla and cornflour (it may look a little split right now but that's fine it'll come good once the flour is added)
Stir in the flour, bicarbonate of soda, malt powder and salt. Bring together to a soft dough
stir in the chocolate chips and then form into 2 equal sized balls and place on the lined baking sheet. Cover and place in the fridge for at least 4 overs, but preferably overnight
Preheat the oven to 200℃. If you can, whilst it's heating pop the cookie dough balls in the freezer to 10 minutes or so. This helps keep the shape.
Sprinkle over the flaky salt and bake for 12-14 minutes
Leave to cool on the baking sheet for 10 minutes before moving to a wire rack