Preheat the oven to 180 C / 400 F / gas mark 4.

Prepare your tines by lining 3 x 6 inch round cake tins with baking paper (using a little vegan butter rubbed around the tins to help the baking paper stick).

Mix together the soya milk and apple cider vinegar to make a vegan "buttermilk". Leave for 5 minutes until it looks as though it has curdles and gone a little lumpy.

In the meantime, melt the vegan butter and sugar in a saucepan over a low heat. Once melted place it to one side to cool before mixing the the vegan "buttermilk".

Next add the flour, cocoa powder, bicarbonate of soda and salt into a large mixing bowl.

Pour the melted butter, sugar, and "buttermilk" into the bowl and fold.

Next add the Guinness and vanilla and again fold together until the cake mix is smooth and bubbly.

Divide the cake mix across the three tins.

Bake for 30-35 minutes or until the cake is pulling away from the sides of the tin and a clean skewer comes out of the centre of the cake clean.

Once cooked, leave the cakes to cool in the tins before turning them out on to a cooling rack and peel off the baking paper.

Let them cool completely before decorating.

To make the frosting, beat the butter until smooth and creamy. Add the rest of the ingredients slowly while you continue to beat the butter until soft and creamy.

Spoon a third of the icing into a piping bag to decorate the top of the cake later.

Level the cakes by cutting off any domed tops.

Spread a teaspoon of the frosting on to a cake board then place the first layer on to the board.

Spread roughly half of the frosting on to the top of the cake, add the next layer the repeat with the other half of the frosting.

Place the final layer on top and press down gently.

Take a cake scraper or palette knife and smooth any overhanging buttercream around the sides of the cake so that the chocolate cake is just peeking through!

To finish, pipe around the top of the cake in any style you wish.

Sprinkle over any cake crumbs to finish.