Preheat the oven to 180ºC. Peel the apples and cut them into thin slices. Reserve half an apple and cut it into slightly thicker pieces. In a bowl, add the butter, sugar, egg, milk and flour with the baking powder. Add the apple pieces that we had reserved without laminating.
Blend with the mixer until a homogeneous dough is formed, spread in a greased mold about 24 centimeters in diameter. Place the apple slices. Bake for 35 minutes at 180ºC.
While preparing the glaze. To do this, heat the water with the sugar and the jam in a saucepan, bring it to a boil, lower the heat and cook it for ten minutes over low heat. Pour over the cake just after it has come out of the oven.