Cook the pasta in boiling salted water for 10-12 minutes. In the meantime peel and finely dice the onion. Heat the fat in a pot and fry the onion in it. Dust with flour and let it sweat on.
Deglaze with broth and milk while stirring and bring to the boil. Add gorgonzola-mascarpone cheese, melt and stir. Season to taste with salt and pepper. Clean the mushrooms and slice finely. Drain the pasta.
Arrange on plates together with the sauce. Spread mushrooms on top. Wash the parsley, dab dry, pluck the leaves from the stalk and cut into fine strips, except for something to garnish.
Sprinkle over the noodles and garnish with parsley.