Easy because it starts with a yellow cake mix, this cake has fabulous coffee and caramel flavor - it didn't last two full days in the fridge because we all kept going back for "just a bite more". This is originally from Pillsbury's website.
Heat oven to 350°F for shiny metal or glass pan (or 325°F for dark or nonstick pan). Spray bottom only of 13x9-inch pan with baking spray with flour.
In large bowl, place cake mix. In 2-cup glass measuring cup, stir 1 1/4 cups warm water and 1 tablespoon espresso granules until granules are dissolved. Add espresso mixture, butter and eggs to cake mix. Beat with electric mixer on low speed 30 seconds; scrape bowl. Beat on medium speed 2 minutes longer. Pour batter into pan.
Bake 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool cake in pan on cooling rack 15 minutes.
Meanwhile, pour 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 wire whisk, until pourable. Set aside while cake cools.
Poke cooled cake every 1/2 inch with handle end of wooden spoon. Pour dulce de leche mixture evenly over cake; spread mixture over top of cake with metal spatula to fill holes. Run knife around sides of pan to loosen cake. Cover; refrigerate 2 hours.
In medium bowl, beat whipping cream and powdered sugar on high speed until stiff. Spread whipped cream evenly over chilled cake. Sprinkle with chopped chocolate. Store covered in refrigerator.