• The recipe can be easily halved and baked in a springform of about 26 cm/ 10 inches.
• Preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit. Line a baking tray of about 30x40 cm/ 12x16 inch with baking paper.

Crumbles in the food processor:

• Place the flour, sugar and cinnamon in the food processor.
• Pulse shortly to mix.
• Add the very cold butter, cut into cubes, and process shortly until you have crumbles.

Crumbles without food processor:

• Mix the flour, cinnamon and sugar in a bowl, place the cold butter cubes on top and cut the butter into the flour until you obtain crumbles.
• If doing this with your hands, only use your fingertips, if you use your palms the butter will get warm too quickly.
• Place the crumble in the fridge until ready to use.
  

Apples:

• There is no need to peel the apples. Clean and chop them into small cubes. Toss well with lemon juice, it will prevent them from getting brown.

Batter:

• Place the soft butter in a bowl and beat until fluffy.
• Add sugar, vanilla sugar or vanilla extract and cinnamon. Mix well.
• Add the eggs, one at a time, mixing well in between.
• Mix the flour and baking powder in another bowl. Add them to the egg mixture in 3 or 4 batches.
• Divide the batter in two equal parts.
• Leave one batch as it is and mix the second batch with the sour cream. Set aside.

Assembling the cake:

• Spread the batter without the sour cream on the prepared tray.
• Spread the apple cubes evenly on top of the batter.
• Spread the sour cream batter over the apples.
• Top the cake with the crumbles.
• Bake the cake for about 50-60 minutes or until golden brown.
• If the cake starts to get brown long before the baking time is over, cover it very loosely with a piece of aluminum foil.
  
  The cake can be made one day in advance.