Preheat your oven to 160C fan. Line a 2lb loaf tin with non stick baking paper.

In a large mixing bowl, cream the softened butter and caster sugar together until pale, light and fluffy. I use my electric hand mixer.

Add your eggs gradually. Mixing thoroughly in between each, also add your vanilla extract.

Fold in your flour, xanthan gum and baking powder. Make sure everything is thoroughly mixed in.

Split the cake mixture into two separate bowls.

In a small bowl, mix your sieved cocoa powder and milk (or hot water) together until perfectly smooth (if hot water allow this to cool). If it doesn't become a paste add a little more liquid until it does.

Once cooled add to one of your bowls of cake mix, mix it in thoroughly.

Then, at ranondon, spoon in your cake mixture into the tin. I tend to spoon one chocolate, followed by one vanilla etc this will ensure you get a marbled effect. Continue till the mixture is used up.

I like to then use a skewer to gently swirl my cake mixture a little more before placing in the oven.

Bake in the oven for 55-60 minutes, until cooked completely through.

Leave to cool in the tin for a while before placing on a cooling rack to completely cool.

Firstly melt your dark chocolate (I do this is the microwave in 20 seconds bursts), put to one side to cool whilst making the rest of the icing.

Place your butter in a stand mixer (or electric hand whisk if you don't have a stand mixer), mix on its own on a high speed for about 5 minutes. The butter should change from a more yellow colour to being a lot more pale.

Add your icing sugar gradually to the butter and mix for a good 3 minutes till fully mixed.

Sieve in your cocoa powder and then mix again until fully combined.

Add in your cooled melted chocolate and mix until dispersed evenly, the colour is a lovely rich chocolate colour and it's a nice thickness to spread. If it's a little too thick (remember, it needs to be easily spreadable), add a tsp of milk and mix it in.

Spread your icing all over your loaf cake and then finish off with sliced Creme Eggs.