Grease and line a deep 20cm x 20cm tin with baking parchment
Make the caramel: put the condensed milk, butter, sugar and syrup into a heavy based pan and melt, over a medium heat, stirring frequently,until the sugar has dissolved, then bring up to boiling
Allow the mixture to gentle boil for 2-3 minutes. Take off the heat, stir in the sea salt and set aside
Put 20g butter into a small, heavy based saucepan. Heat on low-medium, until melted. Add 110g marshmallows and stir with a wooden spoon, until the marshmallows have melted and are thoroughly blended with the butter. Quickly mix in half of the rice krispies
Spoon the marshmallow krispies into the tin, and spread out evenly. Ensure the mixture is pressed down gently but firmly to create a solid layer. The mixture will be very sticky but using a piece of cellophane makes this task much easier.
Give the caramel a stir and pour over the krispie base. Scatter the chopped pecan nuts over the top and place in the fridge for 1-2 hours to set
Using the remaining butter, marshmallows and rice cereal, make another batch of marshmallow krispies and spoon it over the caramel layer. Again, using a piece of cellophane, spread the krispies out and press down gently, but firmly
Leave to firm up for an hour before slicing into squares
Store in an airtight tin. Best eaten within 2 days
Notes
Several readers have requested conversions into American cups. At the time of publishing, I was not confident I had the cup measures right and only go ahead and publish cup measures when I am confident. I hope this doesn't bother you too much. Please remember that I'm offering up my recipes for free. I do not get paid. Please also remember that I am a UK blogger, where grams and ounces are normal measures - not cups. It's just one of our many little differences. I do my best to convert as many recipes as possible for my readers, but sometimes this just isn't possible (blame the butter & marshmallows in this instance).Below is my best attempt at converting this recipe. I'd love to know how you get along if you use these measures. 40g/ 3 tbsp/ ⅙ cup butter 220g/ 8 oz/ 3 cups/ 25 regular vanilla marshmallows -not mini and not jumbo 130g/ 4 ½ oz/ 5 cups rice krispies !For the Salted Caramel 300g/ 10 ½oz / 1 cup condensed milk 75g/ 3oz / ⅓ cup butter 75g/ 3oz / ⅓ cup dark brown sugar 3 tablespoon golden syrup ½ - ¾ teaspoon sea salt (depending on taste) 100g/ 4oz/ 1 cup pecan nuts - roughly chopped