Preheat your oven to 180°C (350°F). Grease a 9-inch round cake pan so the cake doesn’t stick.
Take half a cup of butter (softened) and one cup of sugar. Beat them together until the mixture is light and fluffy.
Beat in two eggs, one at a time, making sure each is fully incorporated. Then stir in one teaspoon of vanilla extract.
In a separate bowl, combine one and a half cups of all-purpose flour, two teaspoons of baking powder, and half a teaspoon of salt.
Gradually fold the dry ingredients into the butter mixture. Alternate adding half of the dry mixture, then half a cup of milk, then the rest of the dry mixture, and finish with the remaining milk. Mix until smooth.
Peel, core, and thinly slice two to three medium apples. You can sprinkle them with one teaspoon of cinnamon if you like.
Pour half of the batter into the prepared pan and smooth it out. Arrange the apple slices evenly over this layer. Then pour the remaining batter on top and smooth the surface.
Place the cake in the oven and bake for 35 to 45 minutes. Check with a toothpick in the center; it should come out clean when the cake is done. Let the cake cool slightly in the pan.
In a small bowl, mix two tablespoons of custard powder with a little cold milk to form a smooth paste. Heat two cups of milk with three tablespoons of sugar in a saucepan until almost boiling. Slowly whisk in the custard paste and cook for 2 to 3 minutes, stirring constantly until it thickens. Remove from heat and stir in one teaspoon of vanilla extract.
Slice the cake and pour warm custard over each portion. Enjoy!