Mix flour, brown sugar, butter, and cinnamon until crumbly. Keep it in the fridge or freezer while preparing the cake so it stays cold.
Make the Cake Batter
In a bowl, mix flour and baking soda together. You can also add cinnamon here if you want. Set this mixture aside.
In the bowl of your mixer, or a large bowl, cream the butter and sugar on medium speed until light. Add eggs, vanilla, and salt and mix until combined. Add the yogurt and mix until all the ingredients are well combined. The batter will look grainy which is normal. Add half of the flour mixture (the flour we just mixed with the baking soda) to the wet ingredients, mix on the lowest setting just until they are combined, then add the rest and mix. Don’t over-mix, always mix on the lowest setting and stop as soon as the flour is mixed. Spread the batter into your baking dish (I used an 18 × 25 cm (7 × 10 inch) dish but the best is 9 x 13 inch).
Prepare the Apples
To make the apples: Peel, core, and slice the apples. Toss them with cinnamon, then spread evenly over the batter.
Bake
Sprinkle the cold crumble over the apples. Bake in a preheated oven at 175°C (350°F) for 40–50 minutes*, depending on your dish size. The larger the dish, the faster it bakes. Remove from the oven and allow to cool at room temperature.
Notes
Nutrition info is estimated and may vary based on ingredients and portions. For the most accurate details, consider using a nutrition tool or checking our full Nutrition Information Disclaimer.
Bake in a preheated oven at 175°C (350°F). I use the fan setting with both the top and bottom heat on, which helps the cake bake evenly and gives the crumble a nice golden top. Place the dish on the middle rack so the heat spreads evenly. Avoid using broil, since that only heats from the top and can burn the crumble before the cake is baked through.
I baked mine in an 18 × 25 cm (7 × 10 inch) dish. You can also use a larger one (which I actually recommend, a perfect size would be 9x13) the cake will be thinner and bake a bit faster, so start checking for doneness around 35–40 minutes instead of 50.