In a city known for sweets, there is little that makes local mouths water more than the towering, historic doberge cake. “It has to be at least six layers,” insists Charlotte McGehee, co-owner of Bakery Bar and Debbie on the Levee, two bakeries in New Orleans, Louisiana, that specialize in doberge (DOH-bash) cake. “In my opinion, fewer than six is just a regular ol’ layer cake. You miss out on that feeling of your fork working through each alternating texture, and the nervousness you get because you don’t want that beautiful…