Start by adding the sugar into a pot that has high sides. Put this pot over medium-low heat.
Keep heating this sugar, whiles stirring, until it has all melted and turned a deep caramel colour.
Take this off the heat and quickly mix in the butter. Then slowly pour in the cream, whiles mixing. Add the salt too.
Place this back onto the heat and let it boil for 1-2 minutes. You just want it to thicken slightly.
At this point, if there are any lumps you can pour this through a sieve, if not just pour straight over the marshmallows. Mix until all the marshmallows have melted.
Now mix in the rice krispies
Grease and line a 9x12 inch cake tin and then add the rice krispie mixture into this and flatten it out. The easiest way to do this is just by using wet hands.
Leave this in the fridge to set. This should take about 1-2 hours. Then just take it out of the tin, cut into it and enjoy.
