Mermaid Birthday Cake

This magical under the sea cake by Trudy Mitchell from JellyCake is guaranteed to be a hit at children's birthday parties!

Make this magical under the sea cake for a seaside themed birthday party for the kids - they're sure to love it!

This Mermaid Birthday Cake by Trudy Mitchell from JellyCake is guaranteed to be a hit at children's birthday parties!

Mermaid Birthday Cake

You will need:

For the cake:

  • 12.5cm (5in) and 18cm (7in) round cakes, each 12.5cm (5in) deep

To decorate:

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  • buttercream
  • 500g (1lb 1oz) mid-blue sugarpaste
  • 800g (1lb 8oz) white sugarpaste
  • 100g (3½oz) light blue sugarpaste
  • 100g (3½oz) pale lilac sugarpaste
  • 100g (3½oz) lilac sugarpaste
  • 100g (3½oz) pale pink sugarpaste
  • 25g (1oz) yellow sugarpaste
  • royal icing
  • 200g (7oz) white sugar florist paste


  • 23cm (9in) round cake drum
  • 13cm (5in) and 18cm (7in) round 3mm (1/8in) cake boards
  • shell template (below)
  • mermaid template (I found mine online)
  • 5 plastic dowels
  • 2 flat wooden lolly sticks
  • black and pink edible pens
  • Sugarflair white pearl lustre dust
  • pink food colour
  • clear alcohol
  • palette knife
  • 4cm (1½in) circle cutter
  • mini flower cutter
  • small plaque cutter
  • number cutter
  • small letter cutters
  • ball tool
  • dresden tool
  • Trex (vegetable fat)
  • edible glue
  • 15mm (½in) pale pink satin ribbon
  • turntable
  • 2 icing smoothers
  • cake side scraper
  • 1 small paintbrush
  • sharp knife/blade
  • foam mat


  1. Trim the tops of the cakes using a large serrated knife to level them. Cut each cake in half, place the bottom layer of each cake on the same size cake card, then spread each half with a layer of buttercream.  Place on each top half and press down lightly. Cover the cakes with a thin layer of buttercream, smooth using a palette knife and place in the fridge for approximately 30 minutes to firm up slightly.Cover the base tier 
  2. Knead the white sugarpaste until you have a soft, pliable dough, then roll out until approximately 3mm (1/8in) thick. Cover the base tier, smoothing all over with the icing smoother and trimming away any excess from the bottom with a sharp knife. Before the sugarpaste is firm, hold one smoother on top of the cake and the other against the side (you can also use flexible acetate style smoothers for this if you have them).  Applying light to medium pressure, run the smoothers around the top edge of the cake until a sharp edge appears. Continue working around the top of the cake until you are happy with the finish.Cover the top tier 
  3. Repeat Step 2 with the blue sugarpaste for the top tier. Then ice the 23cm (9in) cake drum with white sugarpaste and set the cakes and board aside to dry, ideally overnight.
  4. Knead the white sugar florist paste with a little Trex until soft and pliable, then roll out to approx 2mm thick. Place the scallop shell template onto the paste and cut out using the sharp/craft knife. Place on the foam mat and set aside to dry for 24 hours.
  5. Take approx. 50g (1¾oz) of white sugar florist paste and colour to a very pale pink/flesh colour. Roll out to 1-2mm thick. Cut around your mermaid template, then turn it over and cut another mermaid. Place on the foam mat and set aside to dry for 24 hours.
  6. Place some royal icing in the centre of the iced cake board and carefully place the largest tier on the board ensuring it is central. Dowel the base tier with 5 dowels.  Use the royal icing to secure the top cake, ensuring it is central, then leave to set for 30 minutes. When assembling the cake, if you need to move the cakes to ensure they are central to each other, use the icing smoothers to gently move them. Cut the ribbon to fit around the base board and fix with double-sided tape or glue.
  7. Roll out the remainder of the mid-blue sugarpaste to 2mm thick and cut out approx. 20 circles with the 4cm (1½in) circle cutter. Place them under a piece of clingfilm to prevent them from drying out and repeat with the light blue, pale lilac, lilac and pale pink sugarpaste, cutting approx. 20 circles of each. Take 3 circles of each colour and cut in half. Then with the remaining whole circles, use the circle cutter to cut away two quarters from the top of each circle leaving a point at the centre, creating a scale shape. With a little cooled, boiled water, stick the half circles around the very top edge of the cake, leaving a small gap between each one. Then apply the scale shapes, aligning the pointed top into the joins between each of the half circles in the top row. Continue around and down the cake, varying the colours as you go. When you reach the bottom, cut the final row of scales to sit against the base board, then apply.Create the plaques 
  8. Roll out a piece of white sugarpaste to approx. 2mm thick, cut out the small plaque, and using cooled boiled water, fix the plaque centrally on the side of the top tier. Roll out a small amount of pale pink sugarpaste to approx. 1mm thick and using the small alphabet cutters cut out the name(s) of your choice and apply to the plaque with water.Make the tail and clothes
  9. To finish the topper, roll out pale pink and pale lilac sugarpaste and cut a mermaid's tail from each colour using the template (remembering to flip the template over for the opposite mermaid) and adhere to the base of each of the dried mermaid shapes using edible glue, smoothing the sugarpaste over the base mermaid shape to create a soft edge. Do the same for the mermaid’s bra top. Repeat this process with the yellow sugarpaste for the mermaid’s hair and apply as before.  Cut out a small flower from the pale blue sugarpaste and apply to the side of each mermaid’s hair. Using the black and pink edible pens, make little dots for the eyes and a small curve for the mouth. Roll out the lilac sugarpaste and cut a number from the large number cutters. Paint the scallops
  10. Take the pearl lustre dust and mix with a small amount of clear alcohol to make a thin paste. Paint over the front of the scallop shape and, when dry, stick the number to the very centre of the shell using edible glue, then stick the mermaids either side of the number again using the edible glue or royal icing. Leave to set for 1-2 hours.Paint the coral and seaweed
  11. Next make the coral that sits at the base of the top tier below and either side of the plaque. Roll out the pale pink and pale lilac sugarpaste to 2mm thickness. Cut long tapered pieces of paste and twist to look like waving seaweed and apply to cake with water. Cut shorter tapered pieces and dent the surface of the paste with the dresden tool and apply next to the tall seaweed.  Roll small balls of the coloured sugarpaste and stick to the base of the cake with the water. Then using the dresden tool, dent it all over to look like a ball of coral. Take tiny balls of sugarpaste and, using the small end of the ball tool, push it into the ball to create a cup shape and stick to the cake with 4 or 5 others in a small cluster. Make a few more of the ball and cupped clusters of coral for the base of the topper.
  12. Once the topper is set, stand it up on the top of the cake and lightly mark where you would like it to be, making sure to mark the widest points where it sits on the cake. Push the sticks down into the cake, keeping them within the marked area. Apply some royal icing to the front edges of the sticks, then carefully hold the topper against them, press gently to adhere and leave to set. Place the extra coral around the front of the topper and adhere using edible glue or water.

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