Heat the oven to 180C/160C Fan and line three 20cm/8inch cake tins with baking parchment – leave to the side.
In a stand mixer, beat together the butter and light brown sugar until light and fluffy.
Dissolve the Instant Coffee in 2tbsp of Boiling Water.
Add in the flour, pumpkin spice, eggs, and coffee and beat again briefly till combined. Try not to over beat the mixture!
Divide the mixture between the three tins and smooth it over – bake for 25-30 minutes until a skewer comes out clean when poked, and when the cake springs back.
Once baked, leave the cake to cool in the tin for 10 minutes, and then remove and leave to cool fully on a wire rack. If the cake has domed slightly, leave the cake to cool upside down to flatten it slightly.
Beat the Butter on its own in a stand mixer or bowl for a couple of minutes so it's really supple and soft.
Add in the Pumpkin Spice Mix, and the Vanilla, and beat again.
Gradually add in the Icing Sugar until all of it is combined and beat for a good few minutes.
If it's still really stiff, add one tablespoon of boiling water at a time, until its pipeable.
For each layer of the Cake, add a sponge, and slather on some of the Buttercream.
Repeat again with the next layer, and then the final layer.
Spread and smooth some buttercream around the top and sides of the cake - personally I find it easier to do a very thin coat first to seal in the crumbs, put the cake in the fridge for 20 minutes, and then do a thicker layer for the final coat.
Set the cake in the fridge again for 20 minutes.
Melt your dark chocolate carefully until smooth, and stir through 1-2tbsps of oil to loosen slightly - some dark chocolate doesn't need this as it's thinner, but some dark chocolate cake be a little thick and hard to use for a drip.
Carefully drip the chocolate down the sides of the cake with a small disposable piping bag and then cover the top with the rest of the chocolate. Leave the chocolate to sit for a few minutes, and then pipe on some swirls of buttercream.
Sprinkle on your favourite sprinkles and add some spooky marshmallows!