Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and grease and line two 8" cake tins (that are at least 2" deep)
In a mixing bowl, whisk together the vegetable oil and caster sugar
Add the eggs and whisk them in
Then add the vanilla extract, milk and Amarula and whisk in
In another mixing bowl, stir together the self raising flour, cocoa powder and bicarbonate of soda
Add the wet ingredients (the bowl of milk, eggs, Amarula etc) to the flour mixture and whisk in to combine
Divide the mixture between the tins, use scales for accuracy
Bake them for 25-30 minutes or until a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or remove from the tin and place on cooling racks
To make the buttercream, use an electric mixer to mix together the butter and icing sugar until they start to combine, then add the Amarula and mix until smooth
If the cakes have domed on top, level them off with a cake leveller or a serrated knife
Put one of the sponges on your plate or cake stand and pipe or spread some of the buttercream onto it, then spoon over about two thirds of the caramel sauce
Add the other sponge on top and pipe or spread the remaining buttercream on top
Drizzle over the remaining caramel sauce, then add the grated chocolate
Leftovers will keep in an airtight container in a cool place for 2-3 days