Step 4
Meanwhile, spoon dulce de leche into medium microwavable bowl. In small bowl, mix 1/2 cup hot water, 3 tablespoons espresso granules and the rum; stir into dulce de leche until smooth. Microwave uncovered on High 2 to 3 minutes, stirring after about 1 minute with whisk, until pourable. Set aside while cake cools.