Preheat the oven to 170 degrees Centigrade

Grease and line the bottom of both cake tins

In a jug or small bowl mix together the milk, vinegar, oil and vanilla. Set aside

In a large bowl combine the flour, cocoa, sugar, baking powder, bicarbonate of soda and salt

Pour the wet ingredients into the dry, add the yoghurt and stir well until you have a thick but well combined mixture with no lumps of raw flour.

Divide between the two cake tins and level off. Bake for 20-25 minutes until risen and a knife comes out clean.

Remove from the tins and cool on a wire rack.

Whilst the cakes are cooling, make the icing.

Melt the chocolate and leave to cool

Whisk together the margarine, icing sugar and vanilla until light and fluffy.

Whisk in the chocolate until the buttercream is a uniform colour. It will thicken considerably once the chocolate is added.

Use the buttercream the fill and completely cover the cake. Decorate as desired.