Gather all your ingredients in one place, ensuring your butter is at room temperature.

In a medium saucepan over low heat, melt the dark chocolate and butter together, stirring gently until glossy.

In a large mixing bowl, whisk together the eggs and sugar until pale and frothy, about 3 to 5 minutes.

Pour the melted chocolate mixture into the egg-sugar mix, add vanilla extract and salt, and gently fold together.

Preheat your oven to 350°F (175°C). Grease an 8-inch round cake pan and pour in the batter.

Bake for about 25-30 minutes or until a toothpick inserted in the center comes out moist but not wet.