Here is a recipe I have for a chocolate rum cake. It is not quite like the one you describe, but perhaps you could use it as a starting point and experiment until you can recreate the one you seek.
Cake
1/2 cup water
1/2 cup unsweetened cocoa powder
2 teaspoons baking soda
2 cups all purpose flour
1/2 cup cornstarch
1/4 teaspoon salt
2/3 cup butter, softened
1 and 3/4 cups granulated sugar
1 and 1/2 teaspoons vanilla extract
2 large eggs, at room temperature
1 cup sour cream
Frosting
2 cups powdered sugar
1/3 cup unsweetened cocoa powder
2/3 cup butter, melted
1 and 1/2 Tablespoons rum
1 teaspoon vanilla extract
1 to 2 Tablespoons milk
Preheat oven to 350 degrees Fahrenheit. Grease and flour two 9-inch cake pans, and set aside.
Stir the water, cocoa and baking soda together in a saucepan over medium heat, until mixture is smooth. Set aside to cool.
Sift flour, cornstarch and salt into a medium bowl. Beat the butter, sugar and vanilla in a large bowl with an electric mixer at medium speed, until creamy. Add eggs one at a time and beat after each addition until just blended.
With mixer at low speed, beat in the dry ingredients, alternating with the sour cream and the cocoa mixture.
Spoon half of the batter into each prepared pan and bake for 45-55 minutes, or until cake is springy to the touch and tests done (toothpick inserted into the center comes out clean).
Cool in pans on a wire rack for 5 minutes, then turn cakes out onto rack to cool.
To make the frosting, mix the powdered sugar and cocoa in a large bowl. Add the butter, rum and vanilla; beat in enough milk to make a thick, spreadable frosting. Spread one-third of the frosting on the top of one layer, then place the other layer on top and frost top and sides with remaining frosting. Garnish with chocolate curls, if desired.
