01 - Preheat oven to 350°F. Grease an 8-inch round springform pan and line the base with parchment paper.
02 - In a heatproof bowl set over a pan of simmering water, gently melt the chocolate and butter together, stirring until smooth. Remove from heat and let cool slightly.
03 - Whisk in the sugar until combined. Add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract and salt.
04 - Sift in the cocoa powder and fold gently to combine until the batter is smooth and glossy.
05 - Pour the batter into the prepared pan and smooth the top with a spatula.
06 - Bake for 22-25 minutes, or until the edges are set but the center is slightly soft. A toothpick should come out with moist crumbs, not wet batter.
07 - Let the cake cool completely in the pan on a wire rack. It will firm up as it cools.
08 - Once cooled, remove from the pan and dust with extra cocoa powder. Top with fresh berries and a light dusting of powdered sugar if desired.