Pre heat the oven to 180C and grease and line 2 20cm cake tins.
Add the butter and dairy free chocolate to a saucepan. Heat on low until melted and combined. Set aside.
In a large bowl mix the flour, xanthan gum, caster sugar, cocoa powder and bicarbonate of soda. In a separate bowl whisk the eggs and dairy free yoghurt. Add the egg mixture and the chocolate mixture to the dry ingredients along with 100ml boiling water. Whisk with an electric whisk until fully combined.
Divide the mixture between the 2 cake tins and bake in the oven for around 30 minutes, or until a skewer comes out clean. Remove from the oven and set aside to cool.