Start by preheating your oven to 350°F (175°C). Butter a 9-inch springform pan all over, then line the bottom with parchment paper and butter that too, this step makes sure your cake comes out easily.
Add the chopped dark chocolate and butter to a big bowl that can go in the microwave. Heat on half power for 30 seconds at a time, stirring after each burst, until smooth and shiny.
Add both sugars, vanilla extract, and a pinch of salt to the melted chocolate. Whisk everything until it looks like a glossy chocolate syrup.
Crack the eggs in one by one, whisking well after each. This step is key to getting that rich, fudgy texture, so take your time until the batter is silky and smooth.
Lightly dust cocoa powder and fold in softly for a smooth, rich taste.
Pour batter into the pan and flatten the top.
Bake for 20–25 minutes, until the edges are set but the center still jiggles slightly, this keeps the cake perfectly fudgy.
Let the cake cool completely in the pan. Patience pays off here, as it helps with clean slicing.
Run a knife around the edges, release the springform, slice up generous portions, and dig into your decadent chocolate creation!