Preheat oven to 275°F (135°C) and grease a 9-inch (23 cm) springform pan.
2. Step
In a large mixing bowl, add the chocolate and butter. Melt in the microwave at 15-second intervals. Stir often and make sure the chocolate doesn't burn, then set aside to cool for a few minutes
3. Step
Add the egg yolks and the orange zest to the chocolate mixture and stir to combine.
4. Step
In a separate mixing bowl, beat the egg whites on high speed with an electric mixer until very white and foamy. Gradually add the sugar. Continue beating on high speed until soft peaks form.
5. Step
Gently fold ¼ of the egg white mixture to the chocolate mixture. Gently fold in the remaining egg white mixture. Be careful not to deflate the eggs. Stir until fully combined. Some streaks are fine.
6. Step
Pour into prepared pan.
7. Step
Bake in the oven for 45-50 minutes or until the sides of the cake gently pull away from the pan.
8. Step
For the orange whipped cream, beat together heavy cream, orange extract, and sugar.
9. Step
Top with whipped cream and garnish with orange zest.
