Decadence Chocolate and Ricotta Tart

Name: Decadence - Chocolate and Ricotta Tart
Ingredients: Use a 23cm ( 9-10in) tart case with a removable bottom; 1- ½ cups plain flour (200gm); ¼ cup pure icing sugar (40gm); 125 gm (1 stick)chilled unsalted butter, chopped; 1 egg ( 70gm); 1 tablespoon of cold water; 100gm melted dark chocolate; 500gm ricotta; 5 eggs ( 4 separated); 3 tablespoons cornflour; 90gm (1/3 cup) castor sugar; ½ vanilla bean scrapped; Zest of a small lemon