Cook the pasta in well-salted water according to the instructions on the packet.
Cut half the onion into small cubes. Wash, drain and chop the parsley. Drain the mushrooms.
Heat a pan with the oil. Sweat the onions in it. Add the mushrooms and fry until the liquid has evaporated. Now add 150 ml of cream. Season with capers, cayenne pepper, bouillon cubes and lemon juice. Mix the starch with 50 ml of cream and the parmesan and use it to thicken the sauce. Stir in the parsley and season with salt and pepper.