You can assemble this cake in one of two ways. You can stack the two layers on top of each other with some frosting in between, or you can slice each cake layer in half horizontally. This will give you a total of four layers and three layers of filling. Either way is acceptable.
Using a serrated knife, cut the dome off the cake layers, leaving you with flat layers. This is an optional step but will leave you with a nice, flat, professional-looking cake.
Place a tablespoon of frosting in the center of your serving platter. This will act as glue to keep your cake from sliding.
Position one cake layer, top side up, in the center of your platter. Press down gently so the icing sticks.
Fill the cake with about ½ - ¾ cup of frosting, spreading to within ¼ inch of the edge. Use ⅓ - ½ cup per layer if you choose to make a four-layer cake.
Position the second layer, bottom side up, on top of the frosted layer, making sure the edges are even all the way around. Placing the layer bottom side up gives you a flat top surface that is relatively free of crumbs.
Using a pastry brush, brush off any loose crumbs.
Ice the sides and top of the cake with a very thin layer of frosting. This is the crumb coat which will allow you to add a second layer of frosting without worrying about crumbs marring the finish.
Refrigerate the cake for about 15 minutes to let the crumb coat set up.
Ice the sides and top of the cake with the finish coat. This coat can be thicker. Aim for about ¼ inch of frosting.
Decorate as desired.