2) Meanwhile make a quick prawn stock: In a small pot, over medium heat, add the prawn shells and onion. Cover with water and bring to a boil. Reduce the heat and simmer for 20 minutes. Strain into a bowl and discard the shells and the onion.
3) Bring a large pot of water to a boil over high heat and add a generous amount of salt. Add the linguini and cook until just tender, 2 minutes less than instructed on the package. Drain and reserve 120ml of cooking water.
4) Heat a skillet over high heat. Add the prawn and cook until they turn pink and start to caramelize, about 3 minutes. Remove the prawn from the pan to a plate and add the remaining marinade. Let cook a few minutes then add about 240ml of prawn stock and about 120ml pasta water. Continue to cook until sauce reduces by half. Add the zest and juice of the remaining lemon, the butter and the parsley and stir to combine. Adjust seasoning with salt and pepper, to taste. Add in the prawn and pasta and toss to combine with the sauce. Turn out into a serving bowl and serve immediately.