This apple crumb cake features a marbled cinnamon and yellow cake for a twist on a fall favorite! The soft and tender cake is topped with cinnamon apples and a generous amount of salty-sweet brown sugar crumble for what feels like a hybrid between apple crisp and cake.
Peel, core and thinly slice the apples about 1/4" thick. Slice again into small chunks around 1/2" long. This doesn't have to be exact, but smaller apple pieces will bake through faster. Add the brown sugar, cornstarch, cinnamon and salt and toss to combine. Set aside.
For the crumb topping
In a medium bowl, combine the melted butter, granulated sugar, brown sugar, cinnamon and salt and stir to combine.
Use a spatula to stir in the flour until you have a cohesive mixture (it will be slightly stiff and crumbly). Set aside.
For the cake
Preheat the oven to 325 F and line an 8x8 pan with parchment. In the bowl of a stand mixer, combine the cake flour, sugar, baking soda and salt. Mix on low to combine.
Add the softened butter a tablespoon at a time and mix on medium low until the mixture is crumbly with lots of moistened crumbs, about 3 minutes.
In a separate bowl, whisk together the buttermilk, eggs and vanilla extract until smooth.
Stream the buttermilk mixture into the bowl with the flour mixture and mix on medium high for one full minute. Batter will be silky smooth.
For the cinnamon batter
Pour about half the batter back into the wet ingredients bowl (~275g). Add the brown sugar, cinnamon and water and stir until fully incorporated.
To assemble
Using a cookie scoop or large spoon, dollop the plain batter in a checkerboard batter across the bottom of the prepared pan, about 4 dollops per row. Repeat using the cinnamon batter to fill in the holes.
Discard the juice from the apples (or keep for another purpose) and sprinkle apples on top of the batter, reserving just a few for garnish on top.
Use your hands to break up the crumb topping and sprinkle it over the apple layer, aiming for a mix of larger pebbles and finer crumbs.
Top the crumb mixture with the last few apple pieces. Bake for 45-55 minutes or until the cake is fragrant, the crumbs start to look dry and the internal temperature reaches 210 F. If using a glass baking dish, you may need to add an extra 5-10 minutes of bake time.
As the cake is cooling, whisk all the glaze ingredients together until smooth and thick but still runny. Drizzle the glaze over the warm (or cooled) cake and enjoy!
Notes
*As a buttermilk alternative, you can also use:
1/4 cup sour cream or full-fat Greek yogurt + 1/4 cup milk or water.
1/2 cup of whole milk + 1/2 tbsp apple cider vinegarĀ
1/4 cup heavy cream + 1/4 cup water + 1/2 tbsp apple cider vinegar. If you don't have apple cider vinegar, any light colored vinegar or lemon juice will work.
**If you love cinnamon, try boosting this amount from 1 tbsp to 1.5 tbsp for a stronger cinnamon flavor.