Place the cup of sugar in a medium-sized saucepan with 1 cup of water and then sprinkle the gelatine evenly over the top.
Over a medium heat slowly bring it to a boil, gently stirring it a few times to make sure the gelatine doesn't stick to the sides.
Once boiling, turn the heat down to medium/low or low (to where it is just simmering/softly boiling), give it a final stir, and then leave it for 10 minutes.
After the ten minutes is up, pour the mix into a large heatproof bowl.
Whilst the sugar syrup is still hot, set your electric beaters (preferably a stand/bench mixer) to high and beat it until the marshmallow is thick and stiff peaked (around 10 minutes).
Working quickly, spoon it into the cases, on top of the chocolate crackle.
Sprinkle the reserved crackle over the tops.
Place 3 or 4 mini marshmallows on top of each one and then pop them in the fridge to set for at least 30 minutes.
Keep them in an airtight container in the fridge for up to 3 days.