1 1/2 cup sugar
1. Preheat the oven to 300F. Butter a ten-inch spring-form cake pan then line the base with parchment or wax paper. In a large bow add chocolate and butter. Melt in microwave or over hot (not boiling water). Once melted, stir in vanilla then let cool to lukewarm.
2. In a large bowl, beat egg yolks and 3/4 cup of the sugar for 3 minutes or until thick. Using a rubber spatula, fold cooled chocolate into egg-yolk mixture. In a separate bowl, beat egg whites until light and foamy. Gradually beat in remaining sugar until soft peaks form. Gently fold chocolate mixture into egg whites, until just uniform in colour (don't over-stir). Slowly pour the batter into prepared pan.
3. Bake for 1 hour, reduce oven temperature to 250F and bake for 30 more minutes. Surface of cake should be crisp and cracked, and a toothpick inserted into centre of cake should come out clean. Leave cake in oven with oven turned off and door slightly ajar, until cake has cooled completely.
Chocolate Ganache Recipe
