Cook pasta according the packaging directions. Drain and add the string beans and 1 tablespoon butter and stir well.
In a skillet add water and bring to boil point and start adding the butter, tablespoon at the time to emulsify. Once all the butter is melted add the prawns and poach – just below simmer- until the prawns are cooked and turn a nice pink color. Season with salt and pepper.
Remove the prawn leaving the juice in the skillet. Add the pasta with the French string beans to the skillet and stir to coat the fettuccine well.
Place pasta in the middle of the plate and place the prawns over it with any juices.