1/4 cup flour
500ml of low fat or reduced fat milk (fresh, UHT or mixed milk powder)
Heat milk in a large microwave pot for 2-3minutes. Whisk in flour and return to microwave for 1-2 minutes. Remove and whisk. Repeat process of heating and whisking until sauce is desired consistency (the sauce will continue to thicken as it cools so leave slightly runnier than desired)
Add Parmesan cheese, herbs, or other flavours to use as desired.