This cake has been made at Ballymaloe for years. We even have guests who ask for it specifically every time they visit. The fruit sinks to the bottom as it cooks, leaving a light sponge on top with a lovely sugary crust.
Preheat the oven to 400 degrees F. Line the sides and base of a 8 by 8-inch square cake pan with parchment paper.
Using an electric whisk or hand held mixer, whisk the eggs, 6 ounces caster sugar, and vanilla extract in a large bowl, until the mixture is thick and mousse-like, and the whisk leaves a figure of eight pattern, this will take about 5 minutes.
Melt the butter in a saucepan with the milk, and then pour the mixture onto the eggs, whisking continuously. Sift in the flour, cinnamon, and baking powder, and fold carefully into the batter so that there are no lumps of flour. Pour the mixture into the prepared pan, and smooth the surface.
Peel and core the apples, and cut them into thin slices, and then arrange them over the batter. They will sink to the bottom. This is meant to happen! Sprinkle the cake with the remaining 1/2 ounce sugar, and bake in the oven for 10 minutes. Reduce the oven temperature to 350 degrees F, and bake until well risen and golden brown, about 20 to 25 minutes.
Allow the cake to cool in the tin, cut into squares and serve warm. It is delicious with cream!
Raspberry and Pear: Instead of the cinnamon, mix the finely grated zest of 1 orange into the batter. Instead of the apples, sink a half pint of fresh or frozen raspberries, and thin slices of 2 pears into the batter, and cook in the same way.