Cream the sugar and butter well
Beat in the egg.
Sift the flour, baking powder, and salt together.
Fold 1/3 of the flour mixture into the creamed butter. Mix in half the milk. Fold in the 2nd third of the flour. Mix in remaining milk. Fold in remaining flour.
Peel and core the apples. Slice thinly. Toss with the cinnamon, sugar, and lemon juice. NOTE Adjust the sugar to the sweetness of the apples, between 50 and 150 grams.
Grease and flour a rectangular cake pan. Add about 1/3 of the batter and spread it out. Place apples on top of the batter.
Bake in a 350 oven for about a half hour. Wait for cake to start shrinking from the sides of the pan and the apples to be tender.
Top apples with remaining batter. If desired, sprinkle top with some additional cinnamon sugar.