Combine Granulated Sugar (1 1/3 cup) and Water (1/3 cup) in a medium-large saucepan. Heat over medium-high until sugar is dissolved, gently swirling pan once or twice. Do not stir. If any crystals form on the side of the pan, brush away with water and a pastry brush. Allow to cook at a boil until starting to turn an amber color, about 10 minutes.
Once the outer edge starts to turn color, you can gently swirl the pan a couple of times to evenly distribute. Once again, do not stir. When it becomes a deep amber color, remove from heat and whisk in Heavy Cream (3/4 cup). The mixture will bubble vigorously.
Once it has smoothed out, whisk in Unsalted Butter (1/4 cup) and Kosher Salt (1/2 teaspoon). Stir in Spiced Rum (1/4 cup).
Pour into a sealable jar and allow to cool completely prior to storing in the fridge. Enjoy!