Rainbow birthday cake tutorial

Using Rainbow Dust ProGels and Colour Splash concentrated food colouring, Julie Rogerson shows how you can create this fun celebration cake - perfect for a birthday party!

Brought to you by Julie Rogerson

Tips for working with sugarpaste:

  •  When cutting out the small hexagons, roll the paste and leave to sit for a few minutes to firm up first, to prevent distorting the shapes.
  • Lay out the shapes on your workboard before attaching to the cake, to decide on the pattern layout that you want to create.

Tips for colouring sugarpaste: 

  • To colour white sugarpaste to red, start by adding orange gel colour. Once this is mixed completely into the paste, add the red gel colouring and mix thoroughly. This will prevent the sugarpaste from turning pink, as can normally happen when you add red colouring straight into white paste.
  • To ensure the paste is coloured completely, cut the paste in half and check the centre. If you can see any white paste still remaining, continue to knead the paste. Keep checking, until the paste is coloured all the way through.
  • Wash your hands between handling different coloured pastes, to prevent any colour transfer.

Need to stock up on your cake decorating supplies? Visit our store, where you can find a range of products to suit your caking needs, including the Rainbow Dust and Colour Splash ProGels and Renshaw sugarpaste. Why not use different colours to create your own colour scheme and look?!

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You will need


  • 6in round sponge cake
  • 750g buttercream/filling of your choice
  • 750g white chocolate ganache
  • 1kg white sugarpaste
  • Red, orange and yellow Rainbow Dust ProGel colour
  • Green, blue and violet Colour Splash concentrated gel colours
  • Tylose powder
  • Royal icing


  • 10in round cake board
  • 6in round cake card
  • Large rolling pin
  • Cake smoothers
  • Spatula
  • Large serrated knife
  • Metal scraper
  • 2cm hexagon cutter (I used the smallest size from the PME geometric multi-cutter set)
  • 9cm (approx.) heart shaped cutter
  • Wooden skewers
  • Pliers
  • Foam pads for drying
  • Cling film/plastic wrap
  • Large paintbrush
  • 15mm red ribbon
  • Non-toxic glue stick or double-sided tape


Cover the cake board with white sugarpaste and set aside to firm up.
Torte, fill and stack the sponge cake onto the cake card. Crumb coat with an initial thin layer of chocolate ganache and leave to set. Apply a second, thicker coat of chocolate ganache and scrape with a metal scraper to a smooth finish. Leave to set (ideally overnight) before covering. The height of the cake should be 4in (12cm).
Brush a thin layer of boiled water over the ganache to attach paste. Roll the white sugarpaste to a thickness of approx. 4mm. Drape over the cake, securing the top of the sides first, then work around the cake, adhering the paste, by pulling out the pleats gently at the bottom and smoothing it onto the cake with your hand. Trim the excess paste and smooth with cake smoothers. Attach to the covered cake board with a little royal icing.
Divide the remainder of the white sugarpaste into six equal pieces (approx. 75g each). Add a small amount of the different concentrated gel colours to each piece, and knead thoroughly to create the desired shade, adding a little more colour if required.
Create the six different rainbow colours as shown (red, orange, yellow, green, blue, purple).
Roll out each coloured paste, using wooden skewers to ensure they are all the same thickness. Leave to sit on foam pads for a few minutes to firm up a little.
Cut out approximately 35-40 hexagons from each colour, placing them on foam pads.
Cover the cut-out shapes with cling film/plastic wrap until ready to use, to keep them soft/flexible. If they are too dry/firm, they could crack when attaching to the cake.
Apply a thin layer of cooled, boiled water to the sides of the covered cake.
Add the first layer of hexagons to the cake, matching up the sides to touch each other.
Move on to adding the second layer of hexagons, offsetting them to create diagonal stripes around the cake.
Continue to add the hexagons, continuing the diagonal pattern.
Keep adding the hexagons, until the entire sides of the cake are covered, keeping any extras for creating the cake topper. Secure the red ribbon to the edge of the cake board with non-toxic glue or double-sided tape.
Add Tylo powder to the remaining red sugarpaste to help it dry quicker, giving support to the cake topper.
Roll out the red sugarpaste to approx. 2-3mm thick, then gently press the heart cutter onto the paste, to leave an outline (be careful not to cut through the paste at this point).
Using the leftover hexagon shapes, attach to the red sugarpaste, using the heart outline as a guide. You need to cover the entire heart shape, going over the edges.
Position the heart cutter carefully, to ensure it is completely covered with the hexagon shapes and cut out.
Leave the heart shape to dry for a couple of hours on a foam pad.
Attach a wooden skewer to the back of the heart shape, using leftover red paste. Roll out to a thin strip and attach over the skewer and onto the paste at each side with a little water. Leave to dry overnight, or until it is firm enough to stand up without drooping.
Insert the bottom of the skewer into the centre of the cake, to support the cake topper.

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