In a skillet over medium heat place water, butter and brown sugar. Stir well to combine and bring to a simmer. Add sliced bananas making sure to keep them separated. Cook for about 20 seconds and then turn and cook for another 20-30 seconds. Remove pan from heat.
To assemble, place a few vanilla wafers in the bottom of a serving cup. Add a little of the custard. Place a few banana slices on the custard. Place vanilla wafers around inside edge of serving cup, add more custard. Place sliced bananas around inside edge of serving cup, add more custard. Garnish with 1 vanilla wafer and 1 banana slice. Drizzle a little of the brown sugar and butter sauce over the top. Refrigerate for at least 1 hour.