01 -
Turn your oven to 180°C/350°F/160°C with fan, or gas mark 4. Place a sheet of baking paper on the bottom of a 23cm (9-inch) springform tin.
02 -
Melt the chocolate using either a double boiler or microwave. Stir the butter into the warm melted chocolate until it's completely blended.
03 -
Mix the 2 whole eggs with 4 yolks and 75g (a third of a cup) of the sugar. Pour in the melted chocolate, adding orange zest and Cointreau if using. Combine gently.
04 -
In another bowl, froth up the whites of the 4 eggs until they look foamy. Slowly sprinkle in the 100g (half a cup) sugar left and whisk till soft peaks form—don’t over-whip.
05 -
Add a spoonful of egg whites into the chocolate mix to loosen it, then carefully fold in the rest of the whites. Pour into the lined tin.
06 -
Stick the cake in the oven and let it bake for 35-40 minutes. You want it puffy, cracked on the outside, and jiggly in the middle. Let it cool in the tin placed on a rack—it'll sink as it cools.
07 -
Place the cooled cake, still in its tin, on your serving plate. Gently peel off the tin, leaving the dip in the center untouched.
08 -
Whip your double cream until it's soft, then pour in the vanilla and Cointreau if you're using them. Finish whisking until the cream holds its shape but stays plush.
09 -
Spoon the whipped cream into the cake's sunken middle, spreading toward the edges. Lightly dust with cocoa powder using a tea strainer to evenly cover.