Lightly grease an 8 inch diameter Bundt pan, then dust with gluten-free flour. Tap off any excess.

Preheat oven to 180C or 160C (fan).

Using a stand mixer with the paddle attachment, beat the butter and caster sugar, until pale and fluffy. Alternatively, you can make the cake batter, in a large mixing bowl, by hand or with an electric hand whisk.

Add the vanilla extract and eggs, one at a time, to the butter and sugar, and beat until well combined.

Sieve the flour and baking powder together.

Add half the flour to the mixture and gently fold together.

Add half the yoghurt to the mixture and gently mix through.

Add the remainder of the flour, and fold through. Add the remainder of the yoghurt and mix through.

Divide the mixture into six bowls using the measurements above and colour accordingly.

Leave the remainder of the mixture as 'normal'.

Put each of the coloured mixtures into either individual piping bags or plastic food bags, with the corner snipped off. This makes it easier to layer the colours in the bundt pan.

Add the 'normal' batter mixture into the bundt pan, Then pipe the red batter on top, making a wide ring. Then add the orange batter but keep it within the ring of the red batter. Next add the yellow, and so on. Each time keeping the batter within the ring of the one below it.

Bake for 30-40 minutes, until a skewer or toothpick inserted comes out clean.

Let the cake cool in the tin for 10 minutes before turning out onto a wire rack to finish cooling.

When cooled, mix together a runny icing with the icing sugar and cold water; so that it will dribble over the top and sides of the bundt cake, but not completely run off.

Decorate with the sprinkles, then slice it to check out the rainbow!