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