Peel the asparagus, boil in salt water and let cool afterwards. Chop the onion and fry in butter. Sprinkle with flour and pour in 500 ml of white wine and ca 2 l of asparagus broth. Season with salt and saffron and let the béchamel boil. Pile lasagne sheets, asparagus and béchamel alternately into the greased baking pan (green layer alternates with white layer). Spread the béchamel on the top layer. Bake in oven at 160 °C for approximately 45 min.