Preheat the oven to 180C. Grease a 24cm springform cake pan and line the base with baking paper.
Place the chocolate and butter in a bowl set over a saucepan of gently simmering water (don’t let the bowl touch the water). Stir until the mixture is smooth and combined, then remove the bowl from the heat and set aside to cool slightly. Place the egg yolks and sugar in an electric mixer and beat until thick and pale. Stir in the cream, rum, vanilla and cooled chocolate mixture.
Whisk the eggwhites and cream of tartar in a clean, dry bowl until soft peaks form. In 3 batches, gently fold the eggwhite into the chocolate mixture with a metal spoon, trying to keep as much air in the mixture as possible. Spread into the prepared pan and bake for 25 minutes or until a skewer inserted into the centre comes out with a few moist crumbs. Transfer to a wire rack and cool in the pan.
Meanwhile, for the ganache, place chocolate and butter in a bowl set over a pan of simmering water (don’t let the bowl touch the water), stirring until smooth. Remove from heat. Place cream and glucose in a separate pan, bring to just below boiling point. Pour over the chocolate mixture and stir until smooth. Chill for 30 minutes or until thick.
Remove cake from the pan and spread the ganache over the cooled cake. Garnish with silver or gold leaf, if using.