Rainbow Cake Project



  • 6 inch round Mondo pro cake pan
  • 8 inch round Mondo pro cake pan
  • Cake mix/batter to make 2 x 3-4 inch high cakes in above sized tins
  • 10 inch white or black Mondo round cake board
  • 6 inch round Mondo silver compressed cake board
  • 8 inch round Mondo silver compressed cake board
  • Mondo cranked spatula
  • Mondo cake turntable
  • 1 tub of Over the top buttercream in your choice of colour (more required if filling cake layers refer step 2 & 3)
  • 1 large bucket of Over the top buttercream (you can get away with a smaller tub depending on base curb coat colour you choose to do)
  • Piping bag Mondo 45cm for each colour you use
  • Over The Top Sprinkle mixes (we used Jimmies and Pastel Confetti)
  • 10-20 grams of fondant - for fondant rainbow
  • Toothpicks
  • Over The Top Edible glue (optional)
  • Wide plastic drinking straws
  • #12 Piping tips and couplers (optional)


Step 1. Baking

Bake cake according to instructions. 3 x 1 inch high layers of 6 inch and 8 inch rounds. Alternatively, you can use 3-4 inch high cakes without torting (filling) layers with buttercream if you choose.

Let cakes cool and trim to level.

Step 2 - Buttercream filling

Stack cakes on cake board with buttercream in between layers. Makes sure base of cake is stuck to cakeboard using buttercream or melted chocolate. It is easier to torte and cover cakes using piping bag to apply buttercream. Don't over fill piping bag, snip end and pipe onto each layer whilst turning cake turntable to assist with even spread. Smooth buttercream over outside of cake in thin layer with spatula and chill for at least 15 minutes (Crumb coat). This initial Crumb coat layer does not have to be perfect. The aim is to keep the crumbs of the cake from showing in the second layer.

Step 3 - Buttercream cover

Repeat process of covering Crumb coat in smooth layer of buttercream for final outer layer if you want a perfect finish beneath rainbow piping. If you feel confident with your piping you can skip this step and pipe onto crumb coat. Chill final outer layer for 15 minutes. Warm long spatula (or metal cake scraper) and carefully spin cake around on cake turntable whilst scraping outer layer off to achieve desired effect. This will minimise outer layer becoming "dirty" with cake crumbs.

**Alternatively, you can use ganache instead of buttercream if you prefer as outer cover for cake prior to final cover in rainbow layers.


Fix 8 inch cake to 10 inch cake board. Use wide drinking straws as supports to top tier by pushing into 8 inch cake - 1 in centre and 4 within the 6 inch diameter to hold up top tier. Cut excess straw so it is level with top of 8 inch cake.

Step 4 - Rainbow Cover

Prepare each of your buttercream colours in your piping bags. Snip approximately 2cm off the tip of bag and you can pipe dots (refer to diagram) you can also first your bags with couplers and a tip #12 (from 17 piece piping set). Use your cranked spatula (we used the 11.5cm/4.5") to flatten your piped dots. Make sure your spatula is clean prior to flattening different colours. TIP: have a cup of hot water to clean your spatula and wipe with clean paper towel. Continue process until cake pattern covers base layer. PRO TIP: don't forget your Mondo Turntable has a brake on it - its very helpful to spin the cake into position then apply the brake when piping.

Step 5 - Decorations

Prepare fondant or gumpaste according to instructions. Roll out sausages of colours you want for your rainbow. Use the Mondo Fondant smoother to have evenly rolled lengths. Place colours around a guide (i.e. cup or bowl) and build rainbow. Stick each layer to the next using edible glue or a small amount of water. Push two toothpicks into each end and allow to dry TIP: if using fondant then mix a small amount of Tylose to assist with hardening. Prepare on baking paper so it is easy to move without damaging. You can also place in oven for 10 minutes at 25 degrees to assist drying (do not touch until cooled).

Step 6 - Sprinkles and Placing decorations

Pre make some holes for the toothpicks when placing your rainbow topper in so it is less likely to break. Position your rainbow topper and gently push down into butter cream. Use excess white buttercream to make whistle clouds using #12 piping tip. If you have any peaks on your clouds you can soften by using you warmed up cranked spatula to gently push down. Complete your designs using Over the Top Sprinkles.



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