What is the 'best' flour to use for brownies?
Short and sweet... Use cake / pastry flour. At 5-7 % protein vs. 11% for AP vs. 13% + for bread flour, that means a lot less gluten formation. This protein, when mixed with water and subjected to mechanical working is what produces gluten. The higher the protein percentage, the 'tougher' (due to the gluten) the final product. Always use cake or pastry flour when making any type of cake, even brownies. And a little extra egg won't hurt, either.