Why do you use plain flour in brownies?

Brownies are typically made with all-purpose flour, not plain flour. All-purpose flour is a blend of hard and soft wheat flours, and it has a moderate protein content. This makes it ideal for many different baking applications, including brownies. Plain flour, on the other hand, is made from soft wheat flour only, and it has a lower protein content. This makes it more suitable for delicate pastries, such as cookies and cakes.

If you were to use plain flour in brownies, they would be more likely to fall apart and have a crumbly texture. This is because the lower protein content in plain flour does not provide as much structure to the brownies. All-purpose flour is the better choice for brownies because it provides the right amount of structure and chewiness.