Wash the fillet, dab dry and cut into fine slices. Peel and chop the onions. Crush peppercorns with a mortar. Wash asparagus, cut off woody ends. Cut asparagus into small pieces.
Pour into boiling salt water. Season with some sugar and a slice of lemon, cook for 8-10 minutes. Meanwhile, prepare pasta in boiling salted water according to package instructions. Heat the oil in a pan.
Brown the onions and the fillet in it at high heat. Season with salt and crushed pepper. Deglaze with white wine, boil down for 1-2 minutes. Add 400 ml water, bring to the boil. Stir 2 tablespoons mascarpone and starch until smooth and thicken the sauce with it, bring to the boil briefly.
Stir in the remaining mascarpone, season to taste again. Arrange fillet and sauce with asparagus and noodles in portions.