Start by making the marshmallows. Prep everything in advance: split and scrape your vanilla bean, then grease your 9 x 13 inch baking tin using some salted butter. In a separate little bowl, sift together your cornflour and icing sugar, making sure there aren’t any lumps in the mixture. Sprinkle about half of the dry ingredients into the buttered tin, so the powder sticks to the butter. Rotate and tap the tin to evenly coat the bottom and sides, then get rid of any excess by turning the tin upside down over your bin or sink. You want a generous coating to avoid the mallow sticking to your tin. Butter a dough scraper or rubber spatula with butter. Set everything aside for later.
Pour 167ml of water and all the gelatin into a metal bowl {you *can* use glass, but make sure it’s heatproof – I would highly advise metal though!}. Stir this together to make sure the water will be evenly absorbed by the gelatin, then set it aside. N.B. The gelatin will soak it up and set. Don’t worry, we’ll melt it with the hot sugar and then whisk it together again! Attach your sugar thermometer {make sure it doesn’t touch the bottom} to a heavy bottomed saucepan (something like Le Creuset is perfect, or equivalent), and over a medium-low heat, melt together: sugar, 333ml water and corn syrup until the mixture comes to a low steady simmer. Do not stir it. Simply let the mixture mildly bubble until it reaches 240F or the “soft-ball” stage. This may take a while – around 10-15 minutes, but be patient and keep watching your mixture. If you need to turn up the heat to get it there, do so slowly and don’t take your eyes off it.
Here’s where you need to be really careful. Using an electric whisk, whisk the gelatin to break it up {it’ll have set like jelly}. Cover your hands with oven mitts and remove the sugar mixture from the heat. Ask someone else to help by tipping the bowl with the gelatin in towards you at a 45 degree angle. Make sure their hands are also covered, and that there aren’t any children about when doing this.
Pour the hot sugar syrup into the bowl, hitting the side as your go to avoid any unnecessary splashes. You want a slow and steady stream, until all of the sugar syrup is in your bowl.
Add pinch of salt, your vanilla bean {split and scraped} plus the vanilla bean paste then turn on your electric whisk to its lowest setting. Be really careful to stand back from your bowl to avoid getting splashed with hot sugar. Whisk for one minute before increasing the speed.
Slowly increase the speed of your electric mixer and whip for approximately 8-10 minutes, or until your mallow mixture turns white and looks thick and glossy. If they need to be whipped for a little longer, continue to do so until the outside of your bowl isn’t warm to the touch anymore. The mixture should be really thick, and very sticky – similar to marshmallow fluff {and not whipped cream}.
Once the mallows have reached the right consistency, take your pre-buttered dough scraper or a large flexible spatula and scrape the sticky mixture out of the mixing bowl and into the 9 x 13 inch baking pan. Work as fast as you can to get it in the tin, as it tends to dry and set quite quickly. Use the scraper or spatula to even out the top.
Let it set for about 4 hours. If you’re leaving them out for longer {like overnight}, cover with clingfilm.