Made By Mom – Rainbow Cake Marshmallow Fondant

In my last Post, I shared with you the recipes I used to make my fabulous Rainbow Surprise Cake – a towering six layer multi-coloured cake which I baked for my Rainbow and Stars themed Baby Shower.  Although it looked cloud-like and beautiful frosted just in my delicious buttercream icing, I continued to decorate that cake using marshmallow fondant and a whole lot of colourful sparkly creativity!

This is what I created: 

My guests were wowed by the rainbow surprise and the marshmallow fondant decorations were – quite literally – the “icing on the cake”!

So, today I would like to share with you my basic recipe for making the world’s easiest and tastiest marshmallow fondant as well as some tips for using it to decorate your own cakes and sweet treats. 

In my experience, good fondant can make or break a great cake – and people either love it or loath it, so be prepared for some cringes when you slice into your freshly baked fondant-decorated cake.  What most people don’t realise though, is that marshmallow fondant is quite unlike traditional fondant (which requires an incredibly laborious process and typically tastes like inedible, sweet plastic to most people.) Marshmallow fondant on the other hand, is super easy – albeit sticky – to make, and results in a delicious soft texture that can actually reduce the sweet taste of an iced cake. Case in point – at my Baby Shower, not one person left the fondant on their plate – even self-professed fondant loathers!

The recipe itself is as simple as it gets: combine melted marshmallows with icing sugar until you create a dough consistency. 

Seriously, it’s THAT simple! 

To melt your marshmallows, simply fill up a microwavable bowl with about half a standard size bag of marshmallows (mini or large are fine, though white are preferable unless you are looking for a beige coloured fondant or are willing to sort through the coloured marshmallows to make a batch of each colour!). Add a tablespoon of water to the bowl and toss to dampen the marshmallows.  Heat in the microwave at thirty second intervals until the marshmallows begin to fluff up and are easily mixed together.  This usually takes about two minutes, but will vary with your microwave, so keep a keen eye!

Remove the bowl from the microwave and begin to add icing sugar, mixing as you go with a non-stick spatula (you can grease the spatula with a bit of lard or butter if the fondant is sticking too much).  For half a bag of marshmallows, you should need roughly two cups of icing sugar, though this will also vary based on the brand and type of marshmallows you use as well as the humidity in your kitchen. 

If you would like to add in a flavouring oil or food colouring, now is a good time to do that as it will be easier to mix it consistently.  However, if you prefer to make up the whole batch at once you can later divide it into smaller batches and colour and/or flavour each one individually as well. If you are choosing to add in the food colouring or flavour afterward, be sure to wear disposable gloves when you knead it in, otherwise you will end up with more colouring and flavour oils on your hands than on your fondant – and food colouring takes FOREVER to get out of your skin!

Once the icing sugar is mostly incorporated into the melted marshmallow, you can drop the entire mixture onto a work surface powdered with icing sugar and begin to knead it using your hands, much as you would knead the dough for a bread or homemade pasta. Continue to knead until the fondant has reached a consistency similar to that of playdough – if it is too sticky, add more icing sugar, and if it is too dry add more melted marshmallows or a bit of butter or lard. 

Congratulations, you have just made your first batch of marshmallow fondant! 

Fondant is easiest to use while it is at room temperature, so if you have a cake already standing by ready for decorating, now is the time to roll out your base fondant and cover your cake with it.  Alternatively, you can store your fondant in ziplock baggies and keep in the fridge for up to a month.  To soften it for use again, simply knead it in your hands for a few minutes, or heat it in the microwave for a few seconds at a time until it reaches your desired softness. 

Decorating a Cake with Marshmallow Fondant

Now that you have your fondant prepared, your first task will be to roll out a large enough piece of fondant to completely cover your base cake, which should already be completely finished with a thin layer of icing, or a “crumb coating” to ensure that the cake maintains its form and the fondant has something to adhere to.  With our Rainbow Cake, we did this using the Buttercream Frosting. 

Begin to roll out your fondant on a non-stick mat or surface – you may cover your surface with a bit of icing sugar or lard instead to ensure that the fondant doesn’t stick. Your fondant should be approximately 1/8 inch thick, and because marshmallow fondant has a tendency to shrink a little when it dries, it should be rolled out at least half an inch larger than twice the height of your cake plus its diameter (for a round cake) or width/length (for a square or rectangular cake).

Roll your fondant onto your non-stick rolling pin and hold over your cake.  Begin by unrolling one edge just over the base of your cake on one side, and quickly in one motion unroll the fondant out over your cake, ensuring that is more or less centred onto your cake.

Using clean, dry hands and working from one side to the other, gently push out any air bubbles or ripples from the top of your cake.  Then, gently place your hands one either side of your cake and continue to smooth and flatten the fondant to the shape of your cake.  This may seem daunting at first, as the excess fondant will seem to ripple too much, but with a little practice and a calm hand, you will learn to stretch and press the fondant in the middle of each ripple until the cake has an even and smooth covering. 

Using a small, sharp knife, trim your fondant just below the base of the cake (remember, the fondant may shrink a little, so be sure not to cut too much off!

If you have any tears or holes in your fondant, you can try to work them back into one another or patch them up – or, when you will be decorating the cake with a lot of other things (like our Rainbow and Stars Cake) you can simply strategically cover the flaws!

Smoothing out the fondant onto your cake is by far the most challenging part of this process, and will likely take some patience and some practice (mmm . . . more excuses to make cake!), but once you master it, you will be able to make incredibly beautiful and impressive cakes easily and quickly!

Decorating your cake with fondant from this point on becomes much like sculpting with playdough – so here is where you can get creative with modelling shapes, using cookie cutters or even using food colouring mixed with a little lemon juice (or vodka) to paint on details. 

For our Rainbows and Stars Cake, I created a large rainbow by rolling my six colours out into long thin tubes, then arranging them side by side in an arch over the top of the cake and down each side.  I then rolled them flat into one another to create the rainbow effect using a small rolling pin. 

I added yellow fondant stars cut out by a small cookie cutter. By wetting their backs with a daub of water, I was able to easily stick them onto the fondant surface across the back of the cake, above the rainbow – and could also quickly conceal any lumps or bumps!  I did the same with dark blue raindrops across the front of the cake below the rainbow. I formed the raindrops easily by rolling the fondant into small balls then pinching their tops and flattening the whole shape.

To complete the look of a rainbow in the sky (and to cover a somewhat sloppy base to my cake – Shhh . . . it’s our little secret!) I attached mini white marshmallows in cloud formations all around the base and up the sides of the cake using a little leftover buttercream frosting! 

With a little bit of gold and silver edible shimmer dust across the stars, raindrops, and marshmallow clouds, my cake was ready to go!