Put the prawns on a large pie pan or plate and pat them completely dry with a paper towel. Arrange the prawns so they lay flat and are evenly spaced.
Heat a large pan over medium heat. Season the prawns with salt and pepper. Add the butter to the pan. When the foaming subsides, raise the heat to high, and invert the plate of prawns over the pan so the prawns fall into the pan all at once. Cook the prawns, without moving them, for 1 minute. Add the garlic and cook for 1 minute. Turn the prawns over and cook for 2 minutes more. Transfer the prawns to a bowl.
Return the pan to the heat and pour in the vermouth and lemon juice. Boil the liquid until slightly thickened, about 30 seconds. Scrape up any browned bits from the bottom of the pan with a wooden spoon. Stir the zest and parsley into the sauce. Pour the sauce over the prawns, season with salt and pepper to taste and toss to combine.
Divide the prawns among 4 plates or arrange on a platter and serve.