Cream butter and sugar, add the vanilla and then the eggs one at a time, adding a spoonful of flour between each one. Fold in the rest of the flour and cornstarch and enough of the milk to create a mixture that is a soft, dropping consistency.
Alternatively, put all ingredients except milk in a food processor and process to a smooth consistency. Then add milk slowly and pulse to reach soft, dropping consistency.
(Only include the baking powder if you're using the processor method.).
Pour and scrape the batter into 2 - 8" round cake pans that have been buttered and lined with parchment or wax paper. Bake for about 25 minutes, until cakes are beginning to come away from the edges, are springy to the touch on top and a cake tester comes away clean. Leave the cakes in their pans on a wire rack for 10 min before turning out and leaving to cool completely.
When ready to eat the cake, put one layer on a plate, right-way up, spread with jam and scatter fruit on top. Spread a layer of whipped cream on top of frit. Sit the other cake on top and sprinkle with a tbsp or so of sugar.