01 -
Line a 9x13 dish with parchment paper.
02 -
In a big pan, combine butter, sugar, and milk. Use medium heat.
03 -
Let boil until it reaches 234°F. That should take around five minutes.
04 -
Turn off the heat. Mix in the chocolate chips until they're melted and smooth.
05 -
Gently add marshmallows, walnuts, and the vanilla extract.
06 -
Pour the mixture into the prepared pan. Level it out evenly.
07 -
Leave to firm up for 4 hours, or pop it in the fridge to speed it up.
08 -
Slice it and enjoy at room temperature.