DIY Mermaid Pool Cake

Vivienne made a big splash for her 8th birthday… literally! To celebrate, she made her very own homemade mermaid pool cake that captured all the magic of summer fun. Complete with shimmering blue jelly “water,” edible sandy beaches, and a playful dolphin perched on the edge, the cake was every bit as enchanting as she’d hoped. Perfect for summer birthdays and pool parties! Ready to get started? Here’s how you can pool together this fun cake! Disclosure: This post contains an affiliate link, and at no additional cost to you, I’ll earn a small commission if you decide to purchase after clicking through the link. I’ll only ever recommend things that I love and believe will help you, and the decision to purchase is entirely yours!

What you’ll need…

Cakes & fillings

2 x packet cakes. Choose your fave flavour.
Eggs, oil/butter, milk/water (as per packets)
1½–2 batches buttercream (about 750–900 g total)

Decorations

2 packs pink musk sticks (for the “pool fence”).
2 packs blue jelly (prepare ahead; more if you want extra depth).
200 g plain biscuits (e.g., Arrowroot/Marie) for sand.
Lollies: banana lollies (floaties), sour rainbow straps (towels), candy shells, Smarties/M&Ms, raspberry licorice, etc.
Mini cocktail umbrellas. Shop here>>>
Small toys for the pool scene (little doll/mermaid, dolphin, floatie). Shop here>>>

Tools

20–22 cm round cake tins (x2)
Baking paper, cooling rack
Offset spatula & bench scraper
Serrated knife for levelling
Piping bag (optional, for neat buttercream rim)
Food-safe cake board (larger than cake)
Rolling pin or zip-lock bag for crushing biscuits

Make-ahead timeline (stress-free!)

1–2 days before… Bake both packet cakes, cool completely, wrap well, and refrigerate. Make blue jelly and set it in a shallow tray so it’s easy to break up. Cut your Cricut topper (instructions below).

Party morning (or the day before)

Make/soften buttercream. Stack, frost, add musk-stick fence, jelly, sand and decorations. Keep chilled (topper & umbrellas go on just before serving).

Step-by-step Mermaid Cake

1) Bake & stack

Bake the two packet cakes following the box directions. Cool completely. Level the tops with a serrated knife. Add a generous layer of buttercream between the cakes and stack on your cake board.

2) Ice the cake

Spread a thin crumb coat of buttercream all over. Chill 15–20 mins. Add a final smooth coat. Tip: Pipe a low rim (like a shallow dam) around the top edge to help hold the jelly “water.”

3) Build the “pool fence”

Press musk sticks vertically around the sides, snug together.

If your room is warm, chill for 10 minutes to set the buttercream grip.

4) Add the water

Roughly break the set blue jelly with a spoon.

Spoon it into the top centre to form the pool. Mound slightly for a 3D ripple look.

Tuck a few small jelly pieces under the fence edge so it looks “full.”

5) Make the sand

Blitz or crush plain biscuits into fine crumbs.

Sprinkle around the base and a little up the board edge for a natural shoreline effect.

6) Decorate the scene

Umbrellas: Open and push into the jelly/sand.

Lollies:

Banana lollies = floaties
Sour rainbow straps = beach towels/paths
Candy shells/Smarties = shells & beach pebbles
Raspberry licorice = pool noodles

Toys: Set a small doll/mermaid on a “towel,” perch a dolphin on the fence, and add any other mini pool toys.

Add your Cricut name/age topper front and centre (see below). Here’s an SVG you can use to get started with the personalisation.

How to:

Import the SVG into Cricut Design Space. Add text for the name and age; choose a bold, readable font. Resize to ~12–14 cm wide (or to suit your cake). Use the Print and Cut option for a nice flat topper. I then chose to laminate to protect it from the buttercream (and then Vivi could keep it!)

Buttercream (quick ratio)

250 g unsalted butter (soft)
400–450 g icing sugar mixture
1–2 tbsp milk
1 tsp vanilla

Beat butter till pale, add sugar in batches, beat until fluffy; finish with milk & vanilla to spreading consistency.

Pro tips & swaps

Jelly insurance: Make an extra half-batch of jelly if you want a deeper pool. Stability: Keep the cake chilled so the jelly stays bouncy and the fence grips. No musk sticks? Swap for KitKats, Mikado/Pocky, or chocolate finger biscuits. Allergies: Use nut-free lollies/toys; always note non-edible items before serving. Clean cuts: Remove toys/umbrellas/topper before slicing; wipe the knife between cuts. Transport: Chill well; carry in a snug box so the fence doesn’t shift.

Storage

Keep refrigerated (because of the jelly). Best served the same day or within 24 hours. Leftovers: cover and refrigerate up to 2–3 days (remove any non-edible décor first).