Start by greasing an 8-inch round cake pan. Line the base with parchment paper and grease that too. This helps prevent any sticky situations later.

In a large saucepan over low heat, combine the semi-sweet chocolate and the butter. Stir frequently until both are fully melted and combined. Remove from heat and let it cool slightly.

In a separate bowl, whisk together the eggs and egg yolk. Add the granulated sugar and continue whisking until the mixture is thick and pale. This can take about 3–5 minutes.

To the cooled chocolate mixture, stir in the orange zest and vanilla extract. Gradually add the egg mixture, gently folding it in until just combined. Avoid overmixing, as we want to preserve that airy texture.

Gently fold in the cocoa powder, cinnamon, and salt. The batter will be thick and luscious.

Pour the batter into the prepared pan. Bake in a preheated oven at 350°F (175°C) for about 25 minutes. The edges should look firm but the center could still be a bit soft.

Let the cake cool in the pan for about 10 minutes before transferring it to a wire rack. Allow it to cool completely before dusting with confectioners’ sugar. Serve it with whipped cream or fresh berries for an added touch.