Line a rimmed baking tray with parchment (see note). Set a pastry brush and a small dish of water next to the stovetop. Add the sugar, golden syrup (or honey) and water to a small saucepan. Set over medium-high heat and, stirring constantly to dissolve the sugar, bring the mixture to a boil. Once the mixture is boiling, cease stirring and dip the pastry brush in the water and wash down the sides of the pan. Allow the syrup to bubble until it reaches a temperature of 150°C/300°F - about 15-20 minutes.
While the syrup is cooking, add the egg whites and salt to a large mixing bowl or the bowl of a stand mixer fitted with the whisk attachment. Using a hand mixer or stand mixer, whip the egg whites on medium speed until they reach medium peaks.
Once the syrup has reached 150°C/300°F, remove it from the heat. Turn the stand or hand mixer to high and carefully stream the hot syrup into the egg whites. The egg whites will increase in volume and become very light and fluffy. Once all of the syrup is added and the mixture is reaching stiff peaks, whisk in the vanilla.
Dust a clean work surface with cornflour and scrape the nougat out on top of it. Use a bench scraper (or your hands; just note that the mixture is hot) to fold the mixture like a letter. Dust with more cornflour and repeat the motion 3-5 more times, until the nougat is cool and pliable.
Press the nougat over the prepared baking tray until it reaches an even thickness of about 5mm. Top with another piece of parchment and allow to set until it is completely cool - about 30 minutes. Use an oiled knife or kitchen shears (my preference) to cut the nougat into 16 equal pieces, directly through the parchment.
Notes
Edible wafer paper can be used in lieu of parchment paper.
Make Ahead
Stored in an airtight container at room temperature, the nougat will keep for up to 3 weeks.