Clean and chop the leek finely. Melt 1 T margarine in a saucepan and saute the chopped leek for 3-4 minutes.

Slice the mushrooms and add them to the pan; cook for a further 3-4 minutes. Stir the flour into the pan, then slowly add the milk, stirring constantly until thickened. Lower heat and simmer while adding mustard, marjoram and seasoning.

When the noodles are cooked, drain them and toss them with the remaining 1/2 T margarine. Pour the sauce over them.