Grease your baking tray and line it with parchment. Set aside.
Place the 3/4 c - 170 g of butter, 2 c - 500 g of sugar, 1/4 tsp salt (if using salted butter) and 2/3 c - 150 ml of unsweetened evaporated milk in a large heavy bottomed saucepan.
Place on a medium low heat and allow to melt and bring to a gentle boil while stirring continously.
Leave to simmer at a light boil for 4 minutes, lowering the heat if necessary, and keep stirring.
Once the 4 minutes have passed, add 1 tsp of pandan aroma before you add 7 oz - 200 gr of white marshmallows (see note). Keep stirring until the marshmallows have dissolved completely.
Turn the heat down and stir in 8.5 oz - 240 g of white chocolate callets or coarsely chopped chunks, stir until the chocolate has completely melted.
Pour your mixture out into your pre-greased and parchmented baking tray and leave to cool at room temperature for 15 minutes.
Place in the fridge and leave to cool for at least 2 hours. I set mine on some trivets as the baking tray was still very hot and I didn't want to accidentally shatter my fridge shelves.
For best results, leave to cool overnight before cutting into even squares and tucking in.