Preheat oven to 175°C (350°F)
Grease a 6-inch round cake pan with butter and cocoa powder. If it’s not a springform pan, make sure to add parchment around and sticking out the sides.
In a heatproof bowl over simmering water (or in the microwave in 20-second bursts), melt the chocolate and butter together until smooth.
Whisk in cocoa powder until no lumps remain. Set aside to cool slightly.
In a mixing bowl, beat the eggs, sugar, vanilla, and salt on medium-high speed for 3–4 minutes until pale, thick, and doubled in volume.
Gently fold the chocolate mixture into the whipped eggs until just combined. Take care not to overmix.
Pour into the prepared pan, smooth the top, and bake for 35–40 minutes. The top should form a thin crust, and a toothpick should come out with a few moist crumbs.
Allow the cake to cool in the pan for 10 minutes. Loosen the edges with a knife, then further cool on a rack.
Once completely cool, dust with powdered sugar or cocoa powder. Slice and serve.
Source: u/CuddleswithClio -
https://www.reddit.com/r/bakingrecipes/s/uJEBW35XD1