Roux: three colours, three jobs

Equal weights of butter and flour. How long you cook them decides both the flavour and how much they will thicken.

White roux: two minutes, no colour at all. Thickens the most. For Béchamel and anything that should stay pale.

Blond roux: four to five minutes, straw-coloured, smelling of biscuit. Thickens slightly less and tastes of something. For velouté.

Brown roux: eight to ten minutes, hazelnut. Thickens least of all — you need about a fifth more of it — but carries the deepest flavour. For Espagnole.

The rule that saves every sauce: hot liquid into cool roux, or cool liquid into hot roux. Never hot into hot — that is where lumps come from.