Preheat your oven to 375°F (190°C).

In a microwave-safe bowl, combine the dark chocolate and unsalted butter. Microwave in 30-second intervals, stirring in between, until smooth.

Whisk the granulated sugar and large eggs in a separate bowl until thick and pale, about 3-4 minutes.

Gently fold the melted chocolate mixture into the whisked eggs and sugar.

Sift in the cocoa powder, vanilla extract, and salt. Fold until combined, ensuring no dry spots remain.

Grease a round 9-inch cake pan and pour the batter in, smoothing the top with a spatula.

Bake in the oven for 25-30 minutes until the top is set but slightly gooey in the center.

Cool in the pan for 10 minutes before inverting onto a wire rack to cool completely.