Pre-heat your oven to 160C Fan/350F/Gas Mark 4, and grease and line two 8" cake tins (that are at least 2" deep)
Make the sponge by mixing the baking spread and caster sugar together in a mixing bowl until fluffy (around 3 minutes), ideally using an electric mixer. Or mix in a stand mixer with the paddle attachment
Add the eggs and Baileys, and mix until fully incorporated
Add the self raising flour, cocoa powder, and baking powder, and whisk or fold in gently
Divide the mixture between the tins, use scales for accuracy if you like
Bake them for 35-40 minutes or until a thin skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or remove from the tins and place on cooling racks
To make the buttercream mix the butter on it's own until it's smooth and creamy, for 2-3 minutes. Use an electric whisk or stand mixer with the paddle attachment for best results
Add the icing sugar and Baileys. Mix until smooth. If the buttercream is too stiff then you can add a little more milk
If the cakes have domed on top, level them off with a cake leveller or a sharp knife
Put one of the sponges on your plate or cake stand and pipe some of the buttercream onto it
Add the other sponge on top and pipe the remaining buttercream on top
Decorate with the Baileys truffles and chocolate sprinkles
Leftovers will keep in an airtight container in a cool place for 3 days
Video
Notes
Make sure all your ingredients (particularly the butter and eggs) are at room temperature before you start baking.
I used a baking spread for the cake and unsalted butter for the buttercream.
You can use any cocoa powder for this cake, of course the better quality it is, the better flavour it will have. Also do make sure you are using cocoa powder and not a hot chocolate powder.
I decorated the cake with Baileys Truffles, I usually get them from shops like B&M Bargains, Quality Save or Home Bargain. They always seem to have them around Christmas time! You can also get them from Amazon.
Although I provide cup measurements, I highly recommend weighing your ingredients out using digital kitchen scales. It is the most accurate way to measure ingredients and will ensure the best results. Digital scales are very low cost and can be purchased for around £12 ($16.50).
For teaspoon (tsp) and tablespoon (tbsp) measurements, please use measuring spoons and not the type of spoons you eat with. Again this will ensure accuracy and provide the best results.