Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan or line it with parchment paper to prevent sticking.
In a large mixing bowl, whisk together the sifted flour, sugar, baking powder, baking soda, cinnamon, and salt until evenly combined.
In a separate bowl, whisk the eggs and then stir in the vegetable oil until the mixture is smooth and slightly frothy.
Pour the wet mixture into the dry ingredients and fold gently with a spatula until just combined. Be careful not to overmix; the batter should be thick but pourable.
Fold in the chopped apples and toasted walnuts, distributing them evenly throughout the batter. The batter will be chunky with bits of fruit and nuts.
Pour the batter into your prepared cake pan, spreading it out evenly with the back of a spatula. You should see some apple pieces peeking through the surface.
Bake in the preheated oven for about 50 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean. The cake will develop a cracky, crisp crust.
Remove the cake from the oven and let it cool in the pan for 10 minutes, which helps it set and makes it easier to remove from the pan without breaking.
Transfer the cake to a wire rack and allow it to cool completely before slicing. The top will be slightly cracked and fragrant with cinnamon and toasted walnuts.
Slice the cake to reveal tender apple chunks and a moist, layered crumb inside, with the crunchy topping providing a lovely contrast in texture.
Enjoy a slice on its own or with a dollop of whipped cream for a cozy fall treat that captures the flavors and textures of harvest time.
