• Preheat the oven to 200°C/ 400°F. Line a baking sheet of about 30x40 cm/ 12x16 inch with parchment 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.

  250 g all-purpose flour/ 9 oz/ 2 cups + 1 tablespoon + 125 g granulated sugar/ 4.5 oz/ ½ cup + 2 tablespoons + ½ teaspoon cinnamon + 150 g unsalted butter/ 5.5 oz/ scant ⅔ cup

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:

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

  750 g tart apples/ about 5 medium, 1.7 lbs + 2 tablespoons lemon juice

Batter:

• Wet ingredients: 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.

  200 g unsalted butter/ 7 oz/ ¾ cup + 1 ½ tablespoons + 200 g granulated sugar/ 7 oz/ 1 cup + 2 sachets vanilla sugar or 1 tablespoon vanilla extract + 2 teaspoons cinnamon + 6 eggs
• Dry ingredients: Mix the flour and baking powder in another bowl. Add them to the egg mixture in 3 or 4 batches.

  450 g all-purpose flour/ 1 lb/ 3 ¾ cups + 4 teaspoons baking powder
• Divide the batter into two equal parts. Leave one batch as it is and mix the second batch with the sour cream. Set aside.

  300 g sour cream/ 10.5 oz/ 1 ¼ cup

Assemble and bake:

• 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.