Place two tablespoons of corn flour into your measuring cup.
Then fill up the cup with plain flour. I usually pour my flour into the cup because the bag is hard to get a cup in and out of without making a huge mess.
If you are of the dipping and leveling then do that with your flour, then take out 2 tablespoons and add in 2 tablespoons of corn flour. Which ever method is easiest for you.