Preheat the oven to 180C/160C Fan and lightly grease your silicone giant doughnut mould.
Beat together the unsalted butter/Stork & caster sugar until light and fluffy.
Add in the eggs, self raising flour, and vanilla bean extract and beat again briefly until they are all combined. Loosen the mixture slightly with a spoonful of whole milk at a time if needed!
Divide the mixture between the two halves of the mould and smooth it over.
Bake for 25 minutes until the cake is golden and when the cake springs back (a skewer should also come out clean).
Leave the cakes to cool fully in the moulds (I recommend baking them onto a wired tray/the bake shelf, as you want the heat to get to the middle of the cakes).
Buttercream Filling
Beat the unsalted butter with an electric mixer until it is smooth and loose.
Beat the icing sugar in gradually.
Add in the cocoa powder and beat again till smooth and fluffy (again, add in a spoonful of whole milk at a time if needed to soften the buttercream).
Turn one of the cakes out of the mould (so that if you sandwiched them together, the bigger sides are in the middle) and pipe/slather the buttercream onto it.
Turn the other cake onto the top of that one, so you have a giant doughnut shape!
Decoration
Melt the milk chocolate and cover the top of it, like a regular doughnut looks like, and sprinkle on some cute looking sprinkles!
Leave the chocolate to set, and enjoy!
Notes
This cake will last in an airtight container for 3 days!
I personally bought my giant doughnut mould from Lakeland as it was on sale for only £2.49 - but there are others online also!
You can obviously just do a plain buttercream frosting for the middle using 125g softened butter, and 250g icing sugar - but I liked the mix of a vanilla sponge with a chocolate filling/covering!