Line the loaf tin crosswise w/ baking parchment.
Clean, trim & peel 3 apples; cut them into small pieces. Add half of the lemon oil & mix well.
Clean, trim & peel the last apple; cut it into thin slices. Add the rest of the lemon oil & mix well.
Preheat the oven to 160° C w/ fan.
Whip the butter & the sugar w/ the handheld elctric mixer until smooth.
Add the eggs & mix thoroughly.
Mix the flour & the baking powder; add the salt.
Mix flour mess & butter-sugar-egg mess. Add the mascarpone.
Fold in the apple pieces.
Pour the resulting mess into the prepared loaf tin.
Arrange the apple slices on top & cover w/ brown sugar.
Bake in the preheated oven for about 60 min. Make the famous test w/ the wooden pin ... & give it another 5-10 min if necessary.
Let the cake rest in the loaf tin for about 10 min; then lift it out of the loaf tin by help of the baking parchment. Peel off the baking parchment somewhat later as soon as the cake has cooled down.