Roast the walnuts in the oven at 150°C for 15 minutes and roughly chop them up.
Add the sugar, milk, and heavy cream in a microwave-safe bowl, microwave until it's warm, and whisk until the sugar dissolves.
Pour the rum into the mixture, and mix some more. Break each biscuit into 4 pieces, soak the biscuits in the mixture, and set aside for a while.
Cut a 1-liter milk carton a little larger than half the size.
Pack the soaked biscuit pieces into the bottom of the milk carton, being careful not to let them overlap.
Evenly spread the raisins and walnuts (1/6 of the amount each), and lay another layer of the biscuits on top, being careful not to let it overlap.
Repeat Step 6 until the biscuits are all used up (about 6 times) and pour in the remaining mixture.
Cover with plastic wrap and chill in the freezer. Once it sets, peel off the milk carton, and slice it into 8 equal slices.
Story Behind this Recipe
A friend taught me this recipe, which I love very much. After many experimentations and making minor adjustments along the way (I probably made this over 10 times), I finally came up with a recipe that tastes just how I like it.
If you have rum-preserved raisins on hand, you could use the rum which the raisins were preserved in, instead of using ordinary rum. But, if you use the raisins soaked in rum, the flavor of alcohol will be too strong, making it taste bitter. If you don't have a milk carton, use a plastic container lined with a sheet of plastic wrap instead.