Preheat the oven to 160°C. Grease & line the base of a 20 cm round cake tin.
Put the ingredients for the base in a food processor and whiz until you get breadcrumbs-like mixture. Transfer it to the tin, then press down evenly with the base of a spoon.
Push the ricotta through a fine-mesh sieve into a bowl. It should be very smooth now.
Separate the eggs. Mix the sugar with the corn flour, then add the egg yolks one by one, whilst beating it continuously. Stir in the smooth ricotta, then the vanilla essence and sour cream.
Whisk the egg whites until stiff, then carefully fold it into the creamy cheese mixture.
Transfer the mixture into the cake tin, spreading it out evenly.
Bake the cake for one hour, then turn off the oven and allow it to cool down in the oven. (You can open the oven door slightly to prevent further cooking and drying out).
When cooled, put it in fridge overnight,or up to 24 hours.
Meanwhile make the topping: Puree the raspberries then put the mixture into a saucepan. Add the sugar and corn-starch and bring to the boil. Simmer until you get a jam-like syrup, then stir in a small cube of butter. (This could be thick or thin - it’s up to you). If you want it super smooth, then push it through a strainer. Let it cool and set aside until you’re ready to serve.
An hour or so before serving, take the cake out of the fridge and loosen the cake tin. Spread the thick raspberry glaze on top evenly, and put it back to the fridge to set. Remove the cake from the tin and serve.
Alternatively, if the glaze is thin, you can create a dramatic effect by letting it drizzle down the side. In this case, just take the cake out of the tin onto a serving plate and then pour over the syrupy glaze.