Preheat the oven to 175°C (155°C fan bake). Line two 20cm-diameter round cake tins with baking paper.
Whisk the flour, sugar, cocoa, baking soda, salt and baking powder in a large bowl.
Beat the Guinness, yoghurt, oil, eggs and vanilla in a bowl or jug.
Gently add the wet ingredients to the dry ingredients and mix well.
Divide between the prepared cake tins. Bake for 35–40 minutes or until a skewer inserted into the centre comes out clean. Allow to cool for 10 minutes then transfer to a wire rack. If time allows, place the cakes in the freezer to make them easier to ice.
To make the Irish Buttercream, beat the butter until light and fluffy. Gradually add the icing sugar and the Irish cream. Beat for 3 minutes until smooth.
Place one of the cakes on a serving platter and spread with buttercream. Top with the other cake and spread the remaining buttercream over the top and sides of both cakes, piping decorations if desired.
To serve, sprinkle generously with shaved chocolate.
A Table at Tangleby
In this exceptional book, it shares more than 170 delicious dishes, from simple snacks to dinner parties that are guaranteed to impress your guests.