Grandpa Ross's Garlic Prawns

My dad invented this recipe. I think it is made for M's birthday every year!! And whenever he catches lots of prawns!

1 large onion, chopped
1 tablesppon oil
1 kilo green prawns, peeled
about a cup of dry Cinzano (Or 3 glugs as Grandpa put it.)
salt and pepper
cayenne pepper, to taste (we like lots)
300 ml cream
1 tablespoon cornflour
1 tablespoon water
chopped parsley or shallots to garnish

Fry onion in oil till soft.
Add prawns to oil, stir fry until going pink. Add cinzano and allow to simmer a little. Add salt, pepper and cayenne. Add cream, then mix flour and water and stir through to thicken. Stir over rice or pasta. Sprinkle top with chopped parsley or shallots