Preheat the oven to Gas 5, 190°C.
Mix the crushed biscuits with the sugar, cinnamon and melted butter. In a separate bowl, whisk 1 egg while until frothy and fold into the biscuit mixture. Press into the bottom of a 23cm spring-form tin and bake for 7-10 minutes until lightly browned. Cool.
Put the ricotta and whole eggs in a bowl and then blend until smooth. Add the icing sugar, yogurt, lemon zest and juice, flour and vanilla extract.
In a separate bowl, beat the remaining egg whites until they form peaks, and then fold into the cheese mixture. Spread over the biscuit base and bake for 50-55 minutes.
Run a knife around the edge of the cake to loosen. Cool. Remove the tin's sides, cover and chill for at least 2 hours.
Serve cut into slices with fromage frais and fresh berries, dusted with icing sugar.