Start by spreading condensed milk on a wafer disc, completely covering it to the edges. Make sure to spread the condensed milk only on the top side of each wafer disk.
Take another wafer and place it on top of the one that is already covered with condensed milk. Repeat the same instruction by stacking the disks of different colors until you use up the entire pack of wafers.
Once you have assembled the layered cake, place it under a press for approximately an hour. You can use a cutting board on top of the cake and place a few pounds of weight, such as a jar of pickles, on top of the cutting board.