1. Preheat oven to 350˚F. Line an 8 x 8 square baking pan or an 8 inch springform pan with parchment paper and grease the sides of the pan, set aside.

Make your Topping

1. In a bowl add all ingredients together; melted butter, chopped walnuts, white sugar, brown sugar, cinnamon, salt and flour. Using a fork combine together until mixture starts to come together and large crumbs form. Set aside.

Make your Filling

1. In a small bowl add all ingredients together; brown sugar, flour and cinnamon. Mix together until well incorporated, set aside.

Make your Cake

1. Using your stand mixer with the paddle attachment add flour, sugar, baking powder, baking soda, and salt to a large bowl. Mix together to combine ingredients. Next, add your butter in chunks and beat on low speed until the butter is combined and resembles small crumbs, approx. 3 minutes.
2. Add eggs, yogurt, milk and vanilla to the batter, mix on medium speed until the batter comes together and is light and fluffy (scraping down the sides and bottom of the bowl as necessary).

Assemble

1. Spoon half the batter into your prepared pan.
2. Next, add a layer of chopped apples, then sprinkle your cinnamon sugar mixture over the entire cake.
3. Spoon the rest of the cake batter onto the apples and cinnamon sugar mixture. Carefully using a bread knife or an offset spatula, spread out the batter evenly over the entire cake (Note: the cake batter is in thin layers; it’s easier to spoon the batter in 4-5 sections over the apples. This is so you can easily spread the batter out, see image above for reference).
4. Top the final layer with the crumble, spread out evenly over the entire cake.
5. Place in the oven and bake for 30 – 35 minutes or until the top is crisp and the centre is baked all the way through. The cake should spring back a little when pressed.
6. Let cake cool on a cooling rack before removing from the pan.