Milk + white roux. The kindest of the five.
The classic white sauce, mother to Mornay, soubise and every proper lasagne bianca.
Stud half an onion with a bay leaf and a clove; infuse in 500ml milk over low heat for 15 minutes.
Melt 40g butter, whisk in 40g flour, cook 3 minutes with no colour.
Whisk in the strained warm milk in three additions. Simmer 15 minutes.
Season with salt, white pepper and a grating of fresh nutmeg. Pass through a chinois.