6 oz (about 1 cup) bittersweet or dark chocolate2/3 cup (1 1/2 sticks) unsalted butter1 cup granulated sugar (divided)6 tbsp unsweetened cocoa powder7 large eggs, separatedButter and unsweetened cocoa powder, for greasing the pan10-inch (25 cm) round cake pan
Preparation
Preheat the oven to 410°F (210°C).
Grease the cake pan with butter and dust with cocoa powder (to keep it gluten-free).
Separate the egg whites from the yolks.
In a bowl, whisk the yolks with 3/4 cup of the sugar (150g) until light and creamy.
Melt the chocolate and butter together in a double boiler (bain-marie) until smooth, and stir into the yolk mixture.
Add the cocoa powder and mix well.
In another bowl, beat the egg whites until soft peaks form.
Gradually add the remaining 1/4 cup sugar (50g) and beat until stiff peaks form.
Gently fold the egg whites into the chocolate mixture in batches, using upward and inward motions to keep the air in the batter.
Pour the batter into the prepared pan and bake for 20 minutes.
The cake should have a mousse-like texture in the cente.
It will finish cooking out of the oven, thanks to the retained heat.
Once cooled, optionally dust with cocoa powder or powdered sugar before serving.