Marshmallow Weet-Bix Slice

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This iconic Australian Marshmallow Weet-Bix Slice recipe with layers of a crunchy baked Weet-Bix and coconut base, raspberry jam and fluffy sweet marshmallow is the perfect sweet treat that looks impressive, but is super easy to make!

Marshmallow Weet-bix slice on a white cake stand.

With its coconut and Weet-Bix base, layer of raspberry jam and fluffy marshmallow topping (made without eggs!) this nostalgic weetbix marshmallow slice is the perfect party food, fundraiser bake, or after school snack!

Like other classic bakes jam drops, date slice, coconut rough slice and apple and sour cream slice, this old-school recipe is as popular as ever!

Have Weet-Bix that nobody wants? Use up the rest of the Weet-bix packet in these other family favourites: Weet-Bix chocolate slice, lemon Weet-Bix slice, Milo Weet-Bix balls.

Top view of pink marshmallow slice on a white plate.

Why You're Going To Love This Recipe

Basic ingredients - this marshmallow Weet-Bix slice is made with simple, easy to find ingredients.
Versatile - whether you want something a little extra special for an after school treat, or an eye-catching bake for birthday parties, fundraisers, fetes, and bake sales, this marshmallow slice is the perfect recipe!
Old fashioned recipe - when a recipe has stood the test of time, you know it's a good one! And kids just love the squishy marshmallow topping...
Conventional and Thermomix - both methods are written in the recipe card at the end of the post.

What You Need

You only need a handful of basic pantry ingredients to make this classic marshmallow Weet-Bix slice!

Note: Scroll to the recipe card at the bottom for the ingredients quantities and full detailed method.

Ingredients needed to make the recipe, placed in individual bowls.

Weet-Bix - or Weetabix if you are in the UK!
Self raising flour - use store-bought self raising flour or make your own self raising flour by adding 2 teaspoons baking powder to every cup of plain flour.
Desiccated coconut - this adds texture and flavour to the base. Use fine desiccated coconut, not shredded coconut.
Brown sugar - adds a little caramel flavour to the base.
Butter - you can use salted butter or unsalted butter in this slice recipe.
Raspberry jam - or strawberry jam!
Caster sugar - also known as superfine sugar, this fine sugar dissolves quicker than granulated sugar.
Water.
Gelatine powder - this setting agent is the key to a fluffy marshmallow!
Pink food colouring - you only need a drop!

Equipment Required

You don't need any fancy equipment to make this easy slice!

Bowl or Thermomix - for mixing the base.
18cm x 28cm slice tin - greased and lined.
Large saucepan or pot - to make the marshmallow.
Hand held beaters or stand mixer - to beat the marshmallow.
Oven - I use a fan-forced oven. If you use a conventional oven, increase the temperature by 10-20 degrees Celsius.

Pieces of marshmallow slice on a cake stand, with a bite taken out of one.

Step By Step Instructions

This homemade marshmallow Weet-Bix slice is like nothing you can buy in the shops!

Note: Scroll to the recipe card at the bottom for the ingredients quantities and full detailed method.

Step 1 - Make The Weet-Bix Base

Preheat the oven and line your slice tin.

Finely crush the Weet-Bix and place into a bowl.

Add the self raising flour, desiccated coconut, brown sugar and melted butter.

Flour, coconut, brown sugar and melted butter added to the crushed Weet-bix.

Mix until well combined.

The base ingredients mixed together in a bowl.

Press the mixture firmly into the base of the prepared tin then bake in the preheated oven. Set aside to cool while you make the marshmallow topping.

The Weet-Bix base pressed down into a lined slice tin.

Step 2 - Spread Jam Over The Base

Spread the raspberry jam over the top of the cooled base in an even layer.

Step 3 - Make The Marshmallow

To make the marshmallow layer, place the caster sugar, water and gelatine powder into a large saucepan. Mix until dissolved.

Place the saucepan over medium/high heat and stir continuously until boiling. Turn the heat down to a low simmer and simmer without stirring for 10 minutes.

Remove the saucepan from the heat and cool.

Water, caster sugar and gelatine powder in a saucepan.

Pour the cooled liquid into a large mixing bowl (or stand-mixer) and beat until very thick and glossy.

The gelatine mixture once beaten, now fluffy, thick and white.

Add a drop of pink food colouring and beat until the colour is evenly dispersed.

Marshmallow topping with pink food colouring added.

Step 4 - Spread Marshmallow Over The Base

Spread the mixture over the cooled base and chill in the fridge until set.

Marshmallow topping spread on top of the baked base.

Once set, cut into pieces.

Close up of pieces of marshmallow slice on baking paper.

Expert Tips

Use a stand-mixer or electric beaters to whisk the marshmallow - using a balloon whisk and whisking by hand is not recommended as you really need to whisk for quite a while!
Let the mixture cool before beginning to whisk - this will make it easier and quicker to beat the marshmallow until thick and glossy.
Don't stir the sugar mixture once it has boiled - otherwise the syrup can crystallise.
The jam layer is optional - but I highly recommend it!
Use fresh Weet-Bix - for the crunchiest slice!
Storage - store marshmallow Weet-Bix slice in an airtight container in the fridge for up to 5 days.

FAQs

Can I freeze this Marshmallow slice?

No, I do not recommend freezing marshmallow Weet-Bix slice.

Can you over mix the marshmallow?

Yes, you can over mix marshmallow, which can result in it not spreading as easily over the base of the slice. Mix just until it becomes sticky, thick and glossy!