Steep the milk with a piece of onion or garlic and a bay leaf for 15 minutes.
Melt the butter in a saucepan.
Whisk in the flour and cook for a minute.
Gradually whisk in the milk.
Cook, stirring constantly, until thick.
For thick béchamel, use ratio of 2 tablespoons butter + 2 tablespoons flour for 1 cup/250 ml milk
For very thick béchamel for soufflé base: 3 tablespoons butter, 5 tablespoons flour, 1 cup/250 ml milk. It makes the souflee more stable.