So, because flour is the structure for your béchamel, the best way to add more structure is to add more flour. The sauce will thicken some when it cools as well, so don't think that your thickest consistency will be when the sauce is at near-boiling.

How long does bechamel sauce take to thicken?

Whisk the into the thin sauce. Bring to the boil and stir for 5 minutes until your sauce has reached the desired consistency. To make your béchamel thicker without flour, reduce the heat to low and simmer the sauce while stirring.

Why won't my bechamel sauce thicken?

A white sauce will separate if there is not enough added thickener (usually flour or cornstarch) or if it is not heated long enough for the flour to thicken the sauce (it should be cooked and stirred until bubbly, then 1 to 2 minutes more). If a white sauce is separated, try cooking it until bubbly.