Preheat your oven to 375°F (190°C). Lightly butter the bottom and sides of a 9-inch springform pan. Line the bottom with a circle of parchment paper, butter the paper, and dust the inside of the pan lightly with cocoa powder, tapping out any excess.
Fill a small saucepan with 1 to 2 inches of water and bring to a gentle simmer over medium-low heat. Place the chopped dark chocolate and cubed unsalted butter into a large heatproof bowl and set it over the saucepan (ensure the bottom of the bowl does not touch the simmering water).
Stir the chocolate and butter continuously until completely melted, smooth, and glossy. Remove the bowl from the heat and immediately whisk in the granulated sugar, vanilla extract, and fine sea salt until well combined. Let the mixture cool for 5 minutes so it is warm but not piping hot.
Add the room-temperature eggs into the warm chocolate mixture one at a time. Whisk vigorously after adding each egg until thoroughly incorporated. After the final egg is added, continue whisking for 1 to 2 minutes until the batter becomes thick, glossy, and emulsified.
Gently fold in the sifted cocoa powder using a spatula or whisk until just combined. Do not overmix to prevent incorporating too much excess air.
Pour the batter into your prepared springform pan and smooth the top gently with a spatula.
Bake at 375°F (190°C) for 35 to 40 minutes. The torte is done when the edges look set and slightly puffed with a delicate crackly crust, while the center still has a gentle, slight jiggle when tapped. An instant-read thermometer inserted into the center should read between 200°F and 205°F (93°C to 96°C).
Remove from the oven and allow the torte to cool in the pan on a wire rack for 15 minutes (the center will naturally sink slightly as it cools, creating its signature dense structure). Run a thin knife around the edges, unlock the springform ring, and transfer the torte to a serving platter. Let cool completely before serving or refrigerating.