01 - Preheat the oven to 350°F. Grease an 8-inch round springform pan and line the base with parchment paper.
02 - Melt the chocolate and butter together in a heatproof bowl set over simmering water, stirring until smooth. Remove from heat and allow to cool slightly.
03 - In a large bowl, whisk the eggs and sugar until pale and slightly thickened, about 2-3 minutes. Incorporate vanilla extract and a pinch of salt if desired.
04 - Gently fold the melted chocolate mixture into the egg mixture until fully combined.
05 - Pour batter into the prepared pan and smooth the surface evenly.
06 - Bake for 20 to 25 minutes, until the edges are set but the center remains slightly soft. The cake will firm up while cooling.
07 - Allow the cake to cool in the pan for 10 minutes. Run a knife around the edges, release the springform, and cool completely.
08 - Dust the cake with cocoa powder or powdered sugar before serving, if desired.