Servings 25 / Prep time 30 mins / Cook time 15 mins

1. Lightly oil a 9×9 inch baking tin and set aside.
2. Add 125ml of the water to a large mixing bowl and pour in the gelatine powder. Give it a little stir and set aside.
3. In a saucepan, pour in the rest of the water, along with the sugar, salt and golden syrup.
4. Over a medium heat, stir the mixture until the sugar has dissolved.
5. Increase the heat and boil the mixture until it reaches a temperature of between 113°C and 116°
6. Remove from the heat and let it sit for 5 mins.
7. Meanwhile, chop the dark chocolate and add it to a microwaveable bowl. Heat for 1 minute, stir and heat for a further 30 seconds. Stir until melted.
8. Using the whisk attachment on a stand mixer, slowly start mixing the gelatine. You can use an electric hand whisk but the process may take longer.
9. With the mixer on, gradually add the syrup.
10. Once all the syrup has been added, increase the mixer speed until high and whip for around 10 minutes, or until the mixture is thick and starts to pull away from the sides of the bowl.
11. Add the Dulce de Leche flavouring and food colouring (if using) and whip on a high speed until evenly distributed.
12. Pour a third of the marshmallow mixture into your prepared tin and spread using an oiled spatula, or similar.
13. Drizzle over some of the melted chocolate and repeat for the remaining two thirds of mixture.
14. Using a knife, swirl the chocolate into the marshmallow.
15. To set the marshmallow, leave at room temperature for at least 6 hours.
16. Once set, sift together the cornflour and icing sugar and use this to dust your worksurface.
17. Turn the marshmallow out onto your worksurface.
18. Using a sharp, hot knife, slice the marshmallow into 25 squares, rolling each square in the cornflour and icing sugar mixture.
19. You can store the marshmallows in an airtight container for 2-3 weeks.