Pre-heat your oven to 160C Fan/350F/Gas Mark 4, grease and line three 8" cake tins (that are at least 2" deep)
For the sponge, mix together the butter and the caster sugar in a large bowl with a spoon until fluffy, or ideally mix using an electric mixer
Add the eggs and mix in well
Add the self raising flour and mixed spice, and gently mix in until you can't see any flour anymore
Divide the mixture between the tins, use scales for accuracy if you like
Bake them for 30-35 minutes or until a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or on cooling racks
If the cakes have domed on top, level them off with a cake leveller or knife
Make the brandy buttercream by mixing the icing sugar, butter and brandy together until smooth. If it is too stiff you can add a little milk to it (or a bit more brandy!) Put into a piping bag with your chosen nozzle
Put one of the sponges on a cake stand or a serving plate, pipe buttercream all over the sponge, then spoon mincemeat over it. Add the second sponge on top and do the same
Add the final sponge and pipe larger rosettes, top with the mini mince pies if using and sprinkles
Leftovers will keep in an airtight container in a cool place for 2-3 days