Puree half the prawns and chop the rest into medium size pieces.
Heat the oil and butter in a pan and add the finely chopped onion and garlic. Saute over a low to medium heat until softened, then add the pureed prawns and tomato sauce and stir together.
Add the chopped prawns and the brandy. When the brandy has evaporated add the cream and the chopped parsley. Season and keep warm.
Meanwhile cook the pasta in salted boiling water until al dente. Drain well and stir into the sauce then serve straight away.