Which is one of the main ingredients of a roux?

HAL 9000, wrong. Roux is specifically flour and fat (e.g. butter) only, adding milk makes it a white sauce

little b, Do you not eat bread, biscuits or cakes then? 😉

I don't like flour

baymax, Roux is fat and flour. To make white sauce, you add milk to the roux.

I only make bechamel sauce or eclairs from my roux so debated between flour and milk...luckily pressed flour.