Make the gelatine mixture. Soak the gelatin sheets in cold water for 10-15 minutes, then squeeze out well. Put the sheets in a bowl, add the boiling water to the gelatin and set aside.
Make the sugar syrup. Combine the water with the white sugar and a pinch of salt in a saucepan.
Bring the water and sugar to a boil. Boil for 5 minutes with the lid on the saucepan. Measure the temperature to 120 degrees Celsius / 248 Fahrenheit.
Add the gelatin mixture (including the water) to the sugar syrup and stir gently until incorporated.
Using a hand mixer or food processor fitted with a whisk, beat the mixture until thick and fluffy - this really takes a while, so take your time. You will be mixing vigorously for a few minutes before it turns white.
Grease the baking tray with neutral oil. Pour the marshmallow mixture into the tray.
Sprinkle a little powdered sugar on top to prevent sticking and let the marshmallows set in the refrigerator for 4 hours to overnight.
Remove the marshmallows from the pan, sprinkle the other side with powdered sugar and cut into cubes with a sharp knife. Enjoy!