Preheat the oven to 180 degrees C. Grease and line the bottom of a small loaf tin with baking paper.
Sift together the flour and salt, then rub in the butter.
Peel, core and cut the apples into 1cm pieces. Chop the chocolate into small chunks. Stir the apples, chocolate and sugar into the mixture then make a well in the centre.
Beat the egg with the vanilla and 5 tablespoons milk. Gradually work these into the dry ingredients to get a dropping consistency, adding a little more milk if necessary. Pour into the tin and smooth out the top.
Bake in the preheated oven until a skewer comes out clean, about 1 1/4 hours.
A slice of this cake also works well as a dessert, served warm with custard or ice cream!