Step 1: Mixing the Mixes
Get two large mixing bowls and mix each mix separately according to the instructions on each box. I mix mine by hand because the only mixer I have sucks, but if you happen to have more than one mixing bowl and good mixers to go with them, you can use that.
Keep in mind that you are making enough mix for two cakes.
Step 2: Fill Pans
Make sure you split your batter evenly or else you will have two different sized cakes.
Step 3: Swirl
Try not to scratch the edges, you could damage your pan or scrape off the grease, then it will be a challenge to get your cake out later.
Remember, you are swirling, not mixing. If you swirl too much you'll end up with a light brown cake and no swirl.
Step 4: Bake
Never just rely on looks to determine if your cake is done, use a kabob skewer or a toothpick. Insert the toothpick or skewer into multiple places near the center of the cake, if it comes out without any sticky batter stuck to it, then the cake's done.
Step 5: Serve
You can choose to either tell your guests beforehand that the cake is swirled or you can let them find out when they eat it.