To find the flour in the US, check the Asian or gluten free sections of your grocery store or a specialty Asian market. For the cheese, I went with Parmesan. But, I may pick up some Queso Fresco next ...
Stir in two-thirds of the cheese along with the chives, mustard powder, salt and pepper. Make a well in the middle of the dry mixture, then pour in the milk and use a metal spoon to mix it in.