Mix the ricotta and sugar together in a bowl. In a separate bowl, mix the flour, cornflour and baking powder together. Gradually whisk alternate spoonfuls of egg and flour into the ricotta until the mixture is smooth.
Gradually whisk in the oil in a thin steady trickle, then the liqueur or sherry to make a smooth thick batter. Pour the mixture into a greased and base-lined 23 cm (9 inch) springform cake tin. Level the surface then cook in a preheated oven, 180°C (350°C), Gas Mark 4, for 40–45 minutes until well risen and a skewer comes out clean when inserted into the centre of the cake. Allow to cool in the tin, cover and set aside until required.
Mix all the fruits together in a bowl then drizzle over the liqueur or sherry.
When ready to serve, loosen the edge of the cake, transfer to a chopping board and remove the lining paper and tin base. Dust heavily with sifted icing sugar and cut into thin wedges. Serve two per portion with a spoonful of the fruit and a little crème fraîche.