Bring a large saucepan of water to the boil. Once boiling, add the salt, then the pasta and cook it for 2 minutes less than the recommended cooking time.Meanwhile, place the chicken stock in a large frying pan and bring to the boil over high heat. Add the butter and whisk until melted and emulsified, then add a pinch of salt. Whisk in the lemon zest and 2 – 3 tablespoons of lemon juice.Drain the pasta, reserving some of the cooking water and transfer it to the pan with the lemon emulsion. Season to taste with salt and pepper, then toss the pasta until the sauce is reduced enough to create a nice coating around the it.Remove from the heat and stirring continuously, add the parmesan until emulsified. Add more lemon zest or juice if needed. If the pasta sauce gets too thick, add some of the cooking water. Serve immediately. Photography by Kitti Gould.Want more from The Cook Up?• Stream free here at .• Get the show recipes, articles and more.