Butter and flour two 9-inch round baking pans and preheat oven to 350 degrees F.
To make room temperature eggs: Place the eggs in a large liquid measuring cup. Fill the cup with lukewarm water and allow the eggs to sit for 15-20 minutes. Using room temperature eggs will allow for an easier and faster meringue.
In a clean bowl with clean beaters, beat the room egg whites with 2 tablespoons of the sugar until they hold almost stiff peaks. (Do not overbeat until dry looking).
In another bowl cream together the butter, the remaining sugar, and vanilla. Whisk together the flour, baking powder and salt and add the mixture in thirds, alternating with the milk, beating until smooth. Stir in the chocolate chips and 1/3 of the beaten egg whites. Fold in the remaining egg whites with a large spatula until thoroughly combined, and divide the batter between the 2 prepared pans.
Bake the layers in the middle of the oven for 35 minutes or until a skewer tests clean and the cake pulls away from the pan. Let the layers cool for 10 minutes and invert them onto racks to cool completely.
Place a medium bowl and beaters in the freezer for 5 to 10 minutes. The cream will stiffen up quicker in a cold bowl and beaters. Beat the cream with the coffee and sugar until it holds soft peaks, about 5 to 6 minutes.
Beat in the sour cream and rum and beat until stiff but still smooth. Put 1 cake layer on a platter. Spread 1/3 of the cream on top and top with the other layer. Cover the cake with the remaining cream. Decorate with additional chocolate chips. The cake keeps covered and chilled for about 36 hours.
Recipe by Leslie Glover Pendleton. Photography by Nathaniel Crawford - Terminatetor Kitchen.