Roll out your white gumpaste and use a template to cut out the rainbow shape - make more than one just in case. Set aside and allow them to dry.

TIP: Do this step as far in advance as possible. 

Roll out balls of white fondant in different sizes then set them aside to dry.

Line your 7 pans with parchment paper and preheat your oven to 350 degrees Fahrenheit. Divide your batter evenly into 7 parts (1.5lbs each) and dye each part a color of the rainbow: red, orange yellow, green, blue, purple, pink. I used pink to represent the colour we can’t see. Bake each for 30-35minutes and let cool in pans before removing.

Remove your cakes from their pans then level and remove the caramelization from each of the bottoms. Use a 7” upside down cake pan as a guide to remove all of the caramelization from the sides.

Use Sir Squeeze A Lot to shower all of your cakes with simple syrup. Let them sit for a couple of minutes to absorb.

Fill and stack your cakes with Italian meringue buttercream from bottom up in the following order: 

Pink 

Purple 

Blue

Green 

Yellow

Orange

Red

Crumb coat your cake with IMBC using a bench scraper to smooth out the edges then chill your cake in the fridge until firm. Remove your cake from the fridge and Ice again with more IMBC and use a bench scraper to really smooth it out and chill it again. Ice your cake once more and use a cake comb as you would a bench scraper to create grooves in the buttercream. Chill your cake again-n very well.

Divide your remaining buttercream into 4oz portions and colour each part every color of the rainbow except for pink. Place each colour of buttercream into its own piping bag.

Starting at the bottom nook, pipe in a red and orange line then use a bench scraper to smooth it out and chill your cake. Repeat for the next nook with yellow and green then bench scrape and chill. And finally, pipe on the blue and purple and again, bench scrape and chill.

Carefully flip your cake over. Then crumb coat the top and chill until firm.

Clay extrude cords of fondant in each of your rainbow colors.

Apply a pink cake drip to the top of the cake then add more to cover the top of the cake and smooth with an offset spatula.  Use a ruler to make slits in the top of your cake where the rainbow will go so that it does not crack once it is set.

Glue your rainbow cords to your gumpaste rainbow bases with clear piping gel.  Add all the colours except red. Then carefully glue your gumpaste rainbow bases together - back to back using royal icing and popsicle sticks for support. The sticks should extend out the bottom of the rainbow. Allow to dry completely. Insert the popsicle sticks into the top of your cake and carefully push the rainbow down until it sits firmly on top.  Glue a pink cord under the rainbow and 3 red cords to the top to finish the rainbow (this will hide the gumpaste base).

Use royal icing as glue to stick white fondant balls together into clusters then add them to the bottom of the rainbow.