Prepare the béchamel (white sauce
) : melt the butter
in a saucepan, medium flame, and pour the flour
on it while stirring with a wooden spoon until well blended. On a more gentle flame, start pouring a bit of milk
and gently stir until it is incorporated ; keep doing this way with all milk
. Never stop stirring. Reckon about 10 minutes until the béchamel is ready (it must get thick).