Bring a deep pan of water to the boil and salt it generously. Add the pasta, cook for about nine minutes until al dente, then drain.
While the pasta is cooking, roughly chop the peas. Cut the prawns in half down their backs. Melt the butter in a shallow pan, add the oil and then the prawns, letting them cook for two minutes till they curl and turn opaque.
Finely chop the dill fronds. Add the chopped peas, a seasoning of salt and black pepper then continue cooking for a minute or two before adding the drained pasta and dill. Serve immediately.