I use a mix of flour and cornflour/corn starch for these burgers. The cornflour gives a different result to plain flour when frying and you'll find that the surface of the burgers becomes more 'crackly' and puffy than using just normal flour as it concentrates the amount of starch you are using to fry. You can make it with only plain / all-purpose flour if you prefer though. Or you can make it with only cornflour for a super crispy result.