Preheat the oven to 170°C and grease three 23cm cake tins.
Rub the butter into sifted flour and sugar, press into one tin, and bake for 30 minutes.
Increase oven to 190°C and whisk eight eggs with sugar and warm water until fluffy.
Fold flour and ground almonds into the egg mixture and divide between the remaining two tins.
Bake sponges for 15 minutes, then cool on a wire rack.
Whisk six egg yolks with most of the caster sugar until pale.
Whisk four egg whites and fold in the remaining tablespoon of sugar.
Fold melted chocolate, whipped cream, and egg whites into the yolk mixture, then chill.
Whisk additional cream to stiff peaks and stir in almond liqueur.
Assemble by layering sponge halves, liqueur, mousse, and crumbled biscuits onto the shortbread base.
Decorate the top with cream swirls and crystallised violets.