Pre-heat the oven to 190°c. Grease the sides and bottom of your cake tin with butter. Sprinkle the tin with some flour and shake it all around so it covers the sides and bottom. Tip out the excess. Peel and chop up the apples into slices.
Melt the butter in a small saucepan. Set aside. In a mixing bowl, beat half the sugar and the eggs until combined. Slowly add the rest of the sugar until it becomes very thick.
Slice the vanilla pod in half and scrape the vanilla seeds into the batter. Add the pod to the butter and give it a little stir. Leave to infuse for a few mins. Remove the pod from the butter and pour into the batter. Mix to combine.
Mix together the flour and baking powder in a separate bowl. Add into the batter alternatively with the milk. So: flour, milk, flour, milk etc. Throw in the apple slices and whole blackberries.
Pour the mixture into the tin and bake in the oven for 70 minutes (or until the cake has browned and has started to come away from the sides). Leave to cool for 5 minutes in the tin, remove carefully and cool on a wire rack. Dust with icing sugar once completely cool.
Notes
Storage - You need to make sure this dessert is refrigerated once finished with. Place it in a sealable Tupperware or on a plate with some clingfilm. It will keep for a couple of days if refrigerated.Re-heating - You could zap it in the microwave for a minute to warm. That might be nice if you're eating it with the next day with ice cream. A minute or two in a hot oven will also work.Freezing - I wouldn't recommend it as the fruit will just go mushy. It won't be the same as it is fresh. Definitely not worth it!