Preheat oven to 200°C. Grease and line the base of a 20cm springform cake pan.
Place the chocolate, butter and 1 tablespoon sugar in a bowl set over a saucepan of gently simmering water (don't let the bowl touch the water). Stir until the chocolate has melted and the mixture is well combined, then remove the bowl from the pan and set side to cool slightly.
Beat the eggs and remaining sugar in an electric mixer for 10 minutes on medium-high until very thick and pale. Using a metal spoon, gently fold in the flour, then the chocolate mixture, trying to retain as much air as possible.
Pour into the prepared pan and bake in the oven for 12 minutes (the cake won't be completely set at this stage).
Remove the cake from the oven and run a knife around the edge of the pan. Set aside to cool in the pan, then place in the freezer for 4 hours or until set.
Remove the cake from the freezer 1 hour before serving and leave at room temperature to soften.
Meanwhile, for the ganache icing, place the cream in a small saucepan over medium heat and bring to just below boiling point. Place the chocolate in a bowl and pour over the hot cream. Stir together until melted and smooth. Allow to cool for 15 minutes before pouring over the cake.
Cut the cake into slices and serve with Easter eggs, if desired.