Bechamel Sauce

To prevent a skin from forming in the fridge, press plastic wrap directly onto the surface of the sauce.

Whisk constantly while adding milk to prevent lumps.

Cook the roux for a minute or two before adding milk to remove the raw flour taste.

Warm the milk before adding it to the roux for a smoother sauce.

Lasagna

Macaroni and cheese

Gratins (e.g., potato gratin)

Mousses and other desserts (when sweetened)

Adding cold milk to a hot roux, which can cause lumps.

Not cooking the roux long enough, resulting in a floury taste.

Overcooking the sauce, which can make it too thick or scorch.