Not including cake-making, this takes about 30 minutes.
Step 1: What You'll Need
1 dowel, at least 1 1/8" in diameter\
saw, to cut dowel
small finishing nails
pieces of plastic or thin cardboard, such as a plastic cup
Step 2: Making the Pillars
After that dries, measure how tall you want the pillars to be, plus the depth of the cake to get an overall height.
Cut the dowel into 4 pieces of the correct length. Don't worry about doing too much damage to the edges you cut, as both sides will more or less be out of view.
Be sure to make your cuts as level as possible, using a miter box if you have one.
Step 3: Extra Support
Don't leave more than 1/4" of the nail sticking out, because if it's too long you might poke through the bottom into whatever you set th cake on, or it will not sit flush on the bottom.
Step 4: Pillars Go Where?
Tape the side to keep the rolled up shape. Best way is to just wrap the plastic tightly around the pillar, tape it, pull it off.
This is what you will use to cut holes in the cake where the pillars will go.
Step 5: Cutting
Quick math on measurements- look to see how many inches in diameter the top cake is. Then subtract the width of two pillars. The remainder is how much top cake lateral area you have to work with between two cross pillars. Take THAT number, subtract about 1/2" or 1" from each side so you don't run out of room and don't crowd the center.
For example: 8" diameter cake - (2x 1 1/4" pillars)= 5 1/2" left over
5 1/2" - 2" (1" on each side) means that the pillars should be right about 3 1/2" apart across the center of your bottom cake. Or just use what looks good and symmetrical.
Cut the holes by inserting the plastic tube, hitting bottom, and twisting, then sloooooowly pulling it out of the cake.
Wash the frosting off the sides each time or you will start making gory, messy holes much larger than the tube.
Step 6: Decorate!
Now move them both to exactly where you want them to be for the duration of the rest of their cake lives.
Step 7: Insert Tab a Into Slot B....
For extra support, but not 100% necessary, take a sheet of plastic leftover from the cake covers, and poke 4 holes in it for the nails to go through. This will provide a platform for the top cake, but will also be slippery- put some random globs of frosting on the plastic piece too to prevent slipping.
And that's it! Top it with some cutesy little figurine things or something and you're all done.