Heat the oven to 170°C (340°F), conventional heat. Grease a 22–24 cm (9-inch) round springform pan and line the base with parchment.

Melt the chocolate gently over a bain-marie or in short microwave bursts. Let it cool slightly while keeping it fluid and only lukewarm.

Cream the softened butter, icing sugar, and vanilla until pale and smooth. Beat in the egg yolks one at a time, then mix in the melted chocolate.

Whip the egg whites until foamy. Gradually add the granulated sugar and beat until the whites are glossy and hold firm peaks.

Fold one-third of the whipped egg whites into the chocolate mixture to lighten it. Fold in the sifted flour, alternating with the remaining whites, taking care not to overmix.

Transfer the batter to the prepared pan and smooth the surface. Bake for approximately 50–60 minutes, until risen and a skewer comes out with only a few moist crumbs.

Cool the cake briefly in the pan, then remove it and cool completely. Chill it before slicing if you want especially neat, even layers.

Cut the cake horizontally into two layers. Warm the apricot jam until spreadable, brush it over the cut surface, sandwich the layers together, and coat the top and sides with a thin layer.

Boil the sugar and water for about 5–6 minutes, until slightly syrupy. Remove from the heat, cool briefly, and stir in the finely chopped chocolate until smooth and glossy.

Pour the glaze over the center of the cake and spread quickly over the top and sides. Leave the cake at room temperature until the glaze sets, then mark portions with a hot, dry knife if desired.