- Preheat the oven to 180C (160C fan/ Gas Mark 4). Grease and line two 20cm round cake tins with baking paper. 
- In a large bowl, combine the flour, sugar, cocoa powder, baking powder, and bicarbonate of soda. 
- In a separate bowl, whisk together the eggs, buttermilk, oil, and vanilla extract. 
- Gradually add the wet ingredients to the dry ingredients, mixing until just combined. 
- Slowly pour in the boiling water, mixing until the batter is smooth. The batter will be quite liquid. 
- Divide the batter evenly between the prepared cake tins. 
- Bake for 30-35 minutes, or until a skewer inserted into the center comes out clean. 
- Let the cakes cool in the tins for 10 minutes before transferring them to a wire rack to cool completely. 
- To make the fudge icing, beat the softened butter in a bowl until smooth and creamy. 
- Gradually add the sifted icing sugar and cocoa powder, mixing well after each addition. 
- Add the milk, a tablespoon at a time, until the icing reaches a smooth, spreadable consistency. 
- Once the cakes are completely cool, spread a layer of icing over the top of one cake, then top with the other cake. 
- Spread the remaining icing over the top of the second cake. 
- Optional Tips: For a richer flavor, substitute some of the vegetable oil with melted butter. For a vegan version, use plant-based milk and flax eggs. Ensure cakes are completely cool before icing to prevent melting. To increase the fudgy flavour, add chocolate chips to batter.