Preheat oven to 180C or 160C fan-forced (355F).
Brush a springform pan with a knob of butter then line the base with baking paper (parchment).
Make the topping by combining the the sugar and cinnamon in a small bowl. Set aside.
Beat the butter and sugar in a bowl with the electric beater until pale.
Add the eggs one at a time, beating well.
Sift the flour, cinnamon & ginger into a bowl.
Fold 1/3 of the flour mixture into the butter mixture until well combined. Then fold in 1/3 of the milk. Repeat, in 2 more batches, with the remaining flour and milk.
Spoon the cake mixture into the base of the pan and smooth it out with a spatula.
Arrange the chopped custard apple over the top, then sprinkle with the topping mixture.
Bake for 35-40 minutes or until a skewer comes out clean. Check it at 30 mins. Note that tea cakes become dry very easily, so be sure to remove from the oven when it is *just* cooked.
Once cooked, remove the cake from the oven and leave it to cool for 20 minutes before removing it from the tin.