Step 1: Set the oven to preheat to whatever temperature the back of the cake box says. Follow the instructions on the back of the cake box for mixing the batter.
Step 2: (Optional) If you’re using chocolate cake or brownie mix instead of cake mix, fill a bowl with chocolate chips, pop it in the microwave for a minute or two until they’re melted, and mix the melted chocolate into the cake or brownie mix. If there’s anyone else around, this is the point at which they casually show up in the doorway in hopes of licking the melted chocolate off of the spoon. My family has the timing of this down to a science.
Step 3: Grease your three pans (spraying Pam on them works fine) and our a third of the cake or brownie batter into each of them. Use the spoon to spread it around so that it covers the entire bottom of the pan. It will look like there’s not enough batter, but don’t worry- it is.
Step 4: Put the cakes in the oven and let them bake for a little less than half the time it says on the box. (This is because they’re thinner, and you don’t want them to burn.) After that amount of time, test them with a toothpick. If the toothpick comes out mostly clean, the cakes are done. If not, put them back in for a couple more minutes, then try it again.
Step 5: Put the cakes in the refrigerator to cool for 30 minutes to an hour. (You can actually leave them in there for a while longer if you want, depending on how soon you need the cake and what other things you have to get done that day.)
Step 6: Take the ice cream out of the freezer and let it soften. While it is softening, take the cakes out of the refrigerator.
Step 7: The Really Important Part
Cover the entire inside of the container you’re going to use with plastic wrap. You may need to cross two or three long sheets of it over each other to get every part of the container covered. Make sure the plastic wrap overlaps the edges of the container a little. I cannot stress enough how friggen’ impossible it is to ever get that ice cream cake out of the container again if you skip the plastic wrap step.
Step 8: At the bottom of the container, put your first layer of cake. (If you’re using brownies and the layer is crispy around the edges, cut off the edges. This is another point at which people will start appearing and mooching for samples. You won’t be using the crispy edges of the brownie for anything, so let the family eat them. It will keep them out of the cartons of ice cream until you’re done using them, for one thing.)
Step 9: Grab a large spoon and spoon on the first layer of ice cream. It will probably be melting a little bit. This is fine. You’re going to freeze it again anyway.
Step 10: Take the next layer of cake out of the pan, trim the edges if necessary, and put it on top of the ice cream layer. If you want, you can add extra nuts, graham cracker crumbs, or whatever else you’d like instead of or on top of the cake layer.
Step 11: Repeat step 9 with the next flavor of ice cream
Step 12: Repeat step 10
Step 13: Repeat step 9 with the next flavor of ice cream
Step 14: Cover the top of the container with plastic wrap or a lid if it has one, and put it in the freezer. Leave it in there overnight.
Step 15: Use the edges of the plastic wrap to lift the cake out of the container. Then take the plastic wrap off the cake.
You can frost it before serving, or you can just skip the frosting entirely and eat the cake as is. Either way, enjoy!
Optional Extra Step: Instead of frosting the cake, melt another bowl full of chocolate chips and frost the cake with melted chocolate. Then put it back in the freezer for another 10 minutes or so to harden. You end up with this cool, sort of professional-looking shell of chocolate over the cake.