Preheat the oven to 190°C/ 170°C fan/ gas mark 5
First make the shortbread. Beat the sugar and butter together in a bowl until the mixture looks soft and creamy.
Stir in the flour and roll out the dough to a thickness of 3mm.
Stamp out 4 hearts with a 4cm heart-shaped cutter, and another 4 hearts with a 5cm heart-shaped cutter.
Transfer them all to a plate and chill in the fridge for 15 minutes.
Once chilled, use a skewer to prick small holes around each heart to create a decorative border and bake for 15-20 minutes, until just coloured. Transfer to a wire rack and dust liberally with caster sugar.
Now make the mousse. Set the heatproof bowl over a pan of simmering water, making sure the bottom of the bowl does not touch the water.
Put the chocolate pieces, brandy and butter in the bowl and slowly melt together.
Grate in the zest from half the orange and stir in the groud cardamom.
Take the bowl off the heat and set aside to cool.
Beat together the egg yolks and sugar.
Carefully stir this ino the chocolate mixture.
In a separate clean bowl, beat the egg whites until they stand in soft peaks. Fold a third of the egg whites into the chocolate mixture, then fold in the remainder. Divide the mousse between 4 teacups and chill in the fridge for at least 2 hours.
Just before serving, peel 8 thin strips of the remaining zest from the orange. Arrange 2 strips in a heart shape on top of each mousse.
Sprinkle a little gold dust then serve with the biscuits.