Preheat oven to 375°F (190°C). Grease an 8-inch springform pan, line the bottom with parchment paper, and grease the paper.
Melt the chocolate and butter together in a double boiler over gently simmering water until smooth and glossy. Remove from heat.
Whisk the granulated sugar, vanilla bean paste, and coarse sea salt into the warm chocolate mixture.
Vigorously whisk in the room-temperature eggs one at a time until the batter is smooth and slightly emulsified.
Sift the baking cocoa over the batter and gently fold until just combined. Do not overmix.
Pour batter into the prepared pan and bake for 25 minutes until the edges are set but the center remains slightly wobbly.
Cool completely in the pan on a wire rack for at least 2 hours before removing the springform ring and serving.
