Note* I like to make this cake in the late evening before bed, then put it in the fridge to do a light ferment overnight, around 8-12 hours.
Butter a 9-inch springform pan well and set aside.
Make the crumble topping by combining the flour, sugar, almonds, butter, salt in a small mixing bowl. I like to use a wooden spoon or clean hands to cut the butter into the flour and almonds.
In a stand mixer fitted with a paddle attachment, cream the butter and brown sugar for 2-3 minutes until light and creamy. Next, add the eggs one at a time, mixing well after each addition. Now mix in the sourdough starter and vanilla bean paste or extract.
In a medium mixing bowl, whisk together the flour, baking powder, baking soda, apple pie spice, and salt.
Add ½ of the dry ingredients to the stand mixer on low speed until just combined. Then, mix in the milk, and finally, mix in the other half of the dry ingredients until just combined.Fold the apples into the batter. Pour the batter into the prepared springform pan and smooth it out evenly to the edges. Sprinkle the crumble topping all over the top.
Wrap in a double layer of plastic wrap and place in the fridge overnight, or 8-12 hours (less time is fine as well - it won’t affect the cake’s rising).
After 8-12 hours, preheat the oven to 350°F. Once the oven is preheated, remove the cake from the fridge and place it directly in the oven, and bake for 40-45 minutes until a toothpick comes out mostly clean. Cool before serving and enjoy.
