• Preheat the oven to 200'C / Fan 180'C / Gas Mark 6 and place 12 muffin cases in a 12-hole muffin tin.
• In a large mixing bowl, cream the butter and sugar together with an electric whisk until pale and fluffy. Add the eggs, yoghurt and milk and mix again until combined.
• Sift in the flour, cocoa powder, baking powder, bicarbonate of soda and xantham gum. Fold in using a wooden spoon or spatula until combined.
• Spoon the mixture evenly between the 12 muffin cases, and then place in the oven. Bake for 5 minutes and then turn the temperature down to 180'C / Fan 160'C / Gas Mark 4. Bake for a further 15-18 minutes and remove from the oven. Remove the muffins from the oven and allow to cool completely while you make the ganache.

To make the ganache:

• Chop the dark chocolate and After Eight chocolates into small pieces and place in a large bowl.
• Pour the double cream into a saucepan and heat on a very low heat. As soon as the cream starts to simmer (not boil) remove from the heat. Pour over the chopped up chocolate and mix with a spoon until all the chocolate has melted.
• Pour the ganache into a piping bag and set to one side to cool slightly while you prepare the muffins.

To assemble:

• Using a sharp knife, cut a small hole in the centre of the muffin, to around half the depth of the cake, and remove the sponge from the middle.
• Pipe the ganache into the hole until it overflows a little. Place the After Eight on top and leave to set. Decorate with edible glitter to finish if using.