Preheat your oven to 170°C and line a mini-muffin tray with 12 cases.
Warm a mixer bowl with boiling water and dry it thoroughly.
Whisk sugar and eggs on high speed until pale and doubled in volume.
Melt the butter in a saucepan and sift flour with mixed spice into a separate bowl.
Pour melted butter around the edge of the egg mixture while continuing to whisk.
Fold the sifted flour and spice into the mixture in two batches by hand.
Pipe the batter into cases and bake for 10-12 minutes until springy.
Cool cakes on a wire rack and remove the paper cases once cold.
Marinade chopped plums in orange liqueur and set aside.
Melt plain chocolate over a bain-marie and set 12 fresh cases in the muffin tray.
Coat the inside of the cases with chocolate, press cakes inside, set, and peel off paper.
Whisk egg white and sugar over simmering water until thick and glossy.
Remove from heat and whisk until cooled and stiff.
Gradually whisk softened butter into the meringue until smooth.
Fold in orange liqueur and extract, then pipe onto the cakes.
Garnish each cake with a marinated plum piece and gold glitter.