Salted Bourbon Butterscotch sauce:

Butterscotch Crumbs: in a small saucepan, melt sugar on medium low heat. When color changes, stir with a wooden spoon or rubber spatula until completely melted. Lower the heat, add butter to the mix, stir until less bubbles. Add chopped cashews and almonds (if using), mix well. Remove from heat, spread the mixture onto parchment paper. Leave to cool off. Break into small pieces. Use a ziplock bag and a rolling pin to crush butterscotch pieces into crumbs. Store in the fridge.

In a small mixing bowl, mix custard powder with 1/2 cup milk until no lumps, set aside. In a small saucepan, bring the rest of the milk to a boil. Add sugar and constantly mix well. Pour custard milk to the saucepan. Simmer on low heat for 5 mins. Remove from heat, set aside and let cool completely.

In a medium mixing bowl, beat whipping cream to soft peaks. Pour custard milk into the bowl, beat for 1 min. Add butterscotch crumbs into the mix as much as you'd like (although you might want to save some for topping), beat until combined, about 30 secs. Stir in the rum (or bourbon). Keep the bowl in the freezer for one hour.

Working quickly, spread 1/3 of the ice cream in the bottom of an air tight container or 9"x5" pan like mine. Drizzle with 1/4 of the butterscotch sauce. Repeat with two more layers of ice cream and butterscotch sauce.

For the top layer, drop spoonfuls of butterscotch sauce atop the ice cream, then swirl with a toothpick. Finish with more butterscotch crumbs. You'll have some butterscotch sauce left over to drizzle over bowls of ice cream; store this in the refrigerator, rewarming it as you're ready to serve it.