How To Make A Cute Baby Shower Onesie Cake

I am known for many things, but my cake decorating skills (or generally making desserts that are aesthetically pleasing) is NOT one of those things. I make delicious things, but they’re not always pretty and that’s okay. When I try cake decorating, it looks like a two-year-old did it.

And I still didn’t do an *amazing* job on this adorable onesie cake, but I’m PRETTY DARN PROUD OF IT and also think the idea/technique is awesome.

For this shower, the mom-to-be had requested her favorite cake—regular yellow box cake with chocolate frosting. And what mama wants, mama gets.

HOWEVER, this hurt my baker’s soul, so I tried to figure out some way to make it special. Well, and I also made a second (delicious) cake 🙂

While sifting through baby shower cake ideas, I stumbled upon this onesie-shaped cake, and it actually looked super easy so it felt I could tackle it. It’s mainly just some simple cutting or carving of a 9×13 cake and then doing the frosting and just a bit of piping.

Mine is definitely not perfect (definitely looks wonkus in the diaper region especially), but I’ll talk about a few of the techniques I used below.

Cake texture

She’d requested the box yellow cake and chocolate frosting, but you can use any combination of flavors and frostings you want. Definitely make sure it’s a cake texture that you’d be able to cut into shapes, though, not something that will fall apart…I’ve given a couple ideas at the bottom of this post.

It also helps to wrap the cooled cake in plastic wrap and put it in the fridge for like 15 minutes to solidify it a bit.

Ideally you can find a 9×13 pan with super square edges vs. rounded, but if you can’t then there’s still a good way to carve it.

Cake shaping and carving

You start with a 9×13 cake, and then you have two different ways to get your main onesie shape.

The way I think is maybe *best* is the one shown here, where you cut the bottom corners off and those become the sleeves. For me, because my pan edges were too rounded, it wouldn’t have worked. You have to carve a neck hole as well.

Another way, which is what I chose, was to just carve very small sleeves into the sides, and the just slim the cake a bit on the sides to match. You still cut off corners at the bottom, or you can carve the curved leg holes from the start. And of course the neck hole.

How to frost it

I am SO bad at this! But I had a couple tips to help try and make it as smooth and even as possible.

I would recommend buttercream, because it’s pretty sturdy. I microwaved my buttercream frosting a bit, and then gave it a super vigorous stir, so it was soft and easy to spread and also very creamy. This helped it go on more evenly and not have as much texture.

In addition, I used this small offset spatula to spread the frosting. I find it helps me much more easily control the icing and get in the crevices.

Then once I have it fully covered, I got some hot water and dipped the spatula in that, then used the (warm, wet) spatula to go back over and try and smooth the frosting as best I could (you’ll have to dip it in the water multiple times). This is supposed to look like a piece of clothing, so you want it smooth! When you’re done, put it in the fridge for 15 minutes to set.

Also…don’t do this. Yes, that is my *first* onesie cake on the floor. I was so ANNOYED. Had seriously just finished perfecting the frosting, all smooth and creamy! Had to bake another.

The piping to make it a onesie cake

Now for the finishing touches! The lines help really make it a onesie cake, rather than a weird unidentifiable shape. Using a bit of white frosting (or mix up a simple vanilla buttercream), add a bit of gel coloring to whatever shade you want, and mix it together.

You’ll want a small round piping tip or a flatter ribbon-like one (I now have this set of tips), and can use a small or large piping bag (or in a pinch, a sturdy ziploc bag). Small bags are okay for this job, but if you’ll also want to do regular cake frosting or other things, I recommend the large pastry bags.

This post shows some of the individual lines you can do, and has some other cute decorating ideas. I didn’t have the same piping tip they did, so went very basic.

The main lines you need (I mimicked what I saw here):

Edge around *almost* the entire cake (potentially minus the leg holes)
A couple lines to imitate the cute onesie arm shape (that stretches to let you shove babies’ heads and arms into it)
I curved in a little on the leg holes to imitate what the onesie would look like on its own (the butt is bigger than the front, so there’s overlap)
You could add a cute pattern like polka dots, which I’d planned to do but ran out of time and frosting, so just wrote a quick “Baby M” on there

Put it back in the fridge for 10-15 minutes just to let it set (so if you lightly touch it, your finger doesn’t get frosting on it). If you’re not serving it within a few hours, I recommend covering it so it doesn’t dry out.

Some gear that will be really helpful for your onesie cake

I don’t normally do this, but in this particular instance having a few specific tools can make this much easier. Here are the things I found super helpful for transforming a simple rectangle into a onesie cake.

Off-set spatula

Piping tips

Piping bags

Gel coloring

So if you’re looking for cute baby shower cake ideas AND you’re like me and terrible at cake decorating, I think this is the cake for you. Everyone will be super impressed, and only YOU will know how simple it was.

Consider these cakes for your onesie!