Preheat the oven to 170°C (340°F). Grease and line a 23cm (9 inch) cake tin.
Melt the chocolate in a heatproof bowl set over a pot of simmering water. Allow it to cool.
In a large bowl, cream the butter and sugar together until light and fluffy. Gradually add the cooled chocolate and egg yolks.
Whisk the egg whites until stiff peaks form, then fold them into the chocolate mixture gently.
Carefully fold in the sifted flour, then pour the batter into the prepared cake tin.
Bake for 45-50 minutes or until a skewer inserted into the center comes out clean. Let the cake cool completely.
Heat the apricot jam gently until smooth, then spread it over the top and sides of the cake.
For the glaze, heat the sugar and water in a pan until the sugar dissolves. Remove from heat, chop the chocolate and add it to the pan, stirring until smooth.
Pour the glaze over the cake, smoothing with a spatula if needed. Let it set at room temperature.
Serve slices at room temperature, ideally with a dollop of whipped cream.