Preheat your oven to 180 c/ 350 F. Butter a 8 inch round pan , preferably springform or loose bottomed ( the pan I used is in the recommended products below) . Dust well with cocoa powder.
Melt the chocolate in microwave or double boiler. Keep aside.
Separate yolks from whites.
Whip up whites with one tablespoon of the sugar to firm peaks.
With an electric mixer or whisk, beat the rest of the sugar and yolks until fluffy.
Add the ricotta , melted chocolate and corn flour. Beat until smooth.
Using a spatula, fold in about 1/3rd of the egg whites into this mixture.
Fold the rest of the egg whites in gently.
Pour batter into prepared tin, tap against counter to level the top and bake at 180 C/ 350 F for 30-35 minutes. The top will be firm and smooth.
Keep the oven door slightly ajar (with a wooden spoon) and let the tin remain in it for 30 minutes.
Unmould when cool .Serve dusted with icing sugar or with whipped cream.