Spinach Lasagna

• 450 g/ 1 lb of spinach
• 12 sheets of oven-ready lasagne

Pick over and destalk the spinach, then blanch in rapidly boiling salted water for 60 seconds. Refresh in cold water, drain and squeeze out all the moisture you can.

Make a béchamel sauce: melt the butter in a heavy pan and stir in the flour. Cook gently, stirring, for about 1 minute, then add the milk and cook, stirring, until thick and smooth. Cook gently for 20 minutes, stirring regu