Kidspot Kitchen

Kidspot Kitchen

Mermaid treasure birthday cake recipe

Birthday cakes are a centrepiece of any birthday party so choose a birthday cake recipe to match the party theme like this Little Mermaid birthday cake. Find more on Kidspot New Zealand.



Chocolate cake:
This can be made up to a month in advance and kept in the freezer.

  • 500ml water
  • 250g butter
  • 660g caster sugar
  • 40g cocoa powder, sifted
  • 2 tsp bi-carb
  • 4 eggs, lightly beaten
  • 550g self raising flour, sifted


  • 41 cm square cake board, found in cake decorating stores
  • 500g readymade white icing, also known as fondant icing
  • 1m blue glitter fabric
  • 1m threaded sequins, dark blue
  • 1m threaded sequins, light blue
  • 50cm Happy Birthday ribbon
  • Pins to secure ribbon to cake
  • Pink edible glitter icing
  • Food colouring – pink, blue, brown, pink, yellow
  • Candles
  • Sea creatures
  • Paper to write message

Equipment and other items needed:

  • 26cm round cake tin
  • Greaseproof paper
  • Sharp or serrated knife

Approximate timings:

  • To make the cake: 15 minutes preparation time, approximately 50-60 minutes cooking time
  • Covering and decorating the cake: 60-120 minutes (this includes covering the cake board and making decorations)


1. Carefully cut a disc from the top of the cake to create a lid. 2. Use baking paper as a template to cut the cake into a shell shape 3. Cut out a hollow in the centre of the sponge

4. Roll out fondant icing and gently drape over cake 5. Cover the lid with fondant icing 6. Using your hands, mold the icing to the cake and tuck edges in underneath

7. Colour additional fondant icing to create treasure 8. Leave treasures to completely dry 9. Place treasures into the shell cake

Chocolate cake

Preheat oven to 160°C. Line tin with greaseproof paper.

Place water and sugar in a saucepan, heat until sugar dissolves before adding butter and cocoa. Bring to the boil and simmer for 1 minute.

Remove from heat and add bi-carb soda.

Allow to cool for 5 minutes before adding flour and eggs. Mix well.

Bake for approx 50-60 minutes or until a skewer comes out clean.

Allow the sponge to cool slightly in the tin before turning out onto a rack.

Shaping the cake

Cut the top of the sponge and keep to one side as this disk will later be covered with fondant icing and used as the lid.

Prepare an outline of a shell using greaseproof paper, ensuring the outline will meet the edges of the sponge so there is not much cut off.

Have the bottom of the cake (the flattest edge) sitting up and with the stencil on top, cut carefully around the outline with a sharp or serrated knife.

Turn the sponge back over onto a large sheet of greaseproof paper, leaving the stencil on the bottom – later when the cake is transferred onto the cake board, the stencil will ensure the sponge does not touch the fabric.

Using the same knife, cut out a hollow in the centre of the sponge. Use small cuts to prevent accidently cutting through to the bottom, until there is an even and rounded cavity.

Place a small handful of the cut away sponge into a mixing bowl. Add enough milk to create a putty like consistency. Use this to fill in any holes around the sponge and to create a smooth edge. Place in the freezer for 30 minutes to help the sponge set and keep its shape.

Readymade white icing

This is also known as ‘fondant icing’ and can be found in larger quantities in cake specialty shops – they also sell them already coloured if you don’t wish to do that yourself. It will keep for a long time if stored in a cool place (like the freezer) and if it’s wrapped very well (I usually use a few layers of cling film before placing in an airtight container)

Usually the icing is quite firm to touch when you open the packet. Break it into small pieces with your fingers and begin to ‘work’ or ‘massage’ it until you notice is becomes smoother and softer. At this point, bring the icing together and knead as you would a dough until it is soft and smooth (the smoothness reminds me of my kids’ baby bottoms!). Once it’s smooth and soft you are ready to add the colour. Approximately 50g will be used for the ‘human treasures’ with the remaining for the pink shell.

Starting with the pink fondant, flatten a little, press some ‘craters’ into the dough and add a few drops of colour. Going slowly but steady is better than adding too much at once (unless you are after a very bright colour!) until you have achieved the strength of colour you are after. To work the colour into the icing, continue kneading as you would a dough. If the icing starts to stick to the bench use icing sugar, as you would flour to dough. To give the swirled effect, don’t knead the colour into the dough as much.

Roll out the pink icing, using icing sugar to prevent sticking, until it is large enough to cover the sponge. Use the cake tin as a guide to ensure the edges will be covered.

Roll up into your rolling pin gently and transfer to the cake. Gently unravel over the cake, starting from the top until the icing is totally unravelled over the sponge.

Use a piece of excess fondant to press the icing into the hollowed area. Using a sharp knife or kitchen scissors, trim away any excess around the edges – allow 1-2cm extra to tuck underneath. When all the icing has been gently pressed into place, turn the sponge over onto another piece of greaseproof paper, remove the stencil and press down the fondant icing onto the base to neaten. Reposition the stencil onto the base before turning the cake onto the cake board.

Using the left over pink icing, roll out to make two circles – one the size of the lid and one slightly larger to lay onto the top. Cut a circle from greaseproof paper to hold the lid and prevent it from sticking to the base of the cake. Lay the top, larger circle on first and tuck down onto the base. Brush water around the edges of the base icing (to glue them together) before sitting the lid on. Wrap ribbon around the base and secure with a pin. Allow the lid to dry in a warm place if possible.

Use the remainder of the icing to create the ' treasures’. If you have a bead cutter, create some necklaces. Roll out fondant icing to create spoons, forks, knives, cups and plates. Keep on greaseproof paper in a warm place to dry before putting into the hollow (at least 2 hours).

Finishing the cake

Generously sprinkle base and lid with edible glitter.

Place candles on lid.

Fill the hollow with ‘human treasures’ and place lid on top.

Surround cake with water creatures.

Write secret message on paper and roll up with a sea creature before tying with ribbon. Position the lid.


  • Rather than making the fondant icing ‘treasures’, you could hide a piece of jewellery which can also serve as a gift for the party girl.
  • You could also make a square cake and create a treasure box instead of a shell.
  • This recipe was created for Kidspot by Chef Sonia.

From Chef Sonia:

Although I am a qualified chef, I’ve had no formal cake making training. What I have learned is through trial and many errors. I hope that by sharing my knowledge, you can become as confident and as excited about cake making as I am! (without the mistakes!) I think the most important thing is to ‘give it a go,’ you’ll be producing amazing cakes before you know it!

Please feel free to contact me for any questions at or at Chef Sonia & You.

Find more birthday cake recipes