Preheat your oven to 170 degrees Celsius. Grease and flour a 22cm springform cake pan, or line with parchment paper.
2
Melt the dark chocolate and unsalted butter together in a heatproof bowl set over a pot of simmering water (bain-marie), stirring until smooth. Remove from heat and let cool slightly.
3
In a large bowl, whisk the eggs, granulated sugar, orange zest, and fine sea salt with an electric mixer until light, pale, and fluffy, about 5-7 minutes.
