Melt butter in a pot. Stir in flour and sweat briefly. Add milk and stock while stirring and let simmer for 5-8 minutes while stirring. Season sauce with salt and nutmeg.
Pour the pasta into a flat casserole dish so that the bottom is covered. Wash the asparagus, cut off the woody ends. Cut the asparagus into pieces about 5 cm wide. Spread on the noodles, sprinkle about 2/3 cheese on top.
Pour the sauce on top and sprinkle the remaining cheese on top.
Bake the casserole in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 30 minutes. Remove the casserole from the oven and serve.