Gather all ingredients.
Place chocolate in a medium mixing bowl.
Heat cream in a small saucepan over medium heat. Bring just to a boil, watching very carefully because if it boils for even a few seconds, it will boil out of the pot.
As soon as the cream comes to a boil, pour it over the chocolate in the mixing bowl. Whisk until chocolate has melted and mixture is smooth, then stir in rum.
To use ganache as a cake glaze, cool slightly, 5 to 10 minutes. Start pouring glaze at the center of the cake and work outward.
For a fluffy frosting or chocolate filling, allow it to cool until thick (up to 1 hour in the refrigerator), and then whip until light and fluffy. Apply it with a spatula like a conventional frosting.
