Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan by lightly coating it with non-stick spray or butter.

Cream together the softened butter, granulated sugar, and dark brown sugar until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, mixing on low speed, then add the vanilla extract and mix until combined.

Gradually add the flour, baking soda, ground cinnamon, and salt to the creamed mixture, mixing until just combined.

Gently fold in the chopped apples and walnuts into the batter using a large spatula.

Pour the batter into the greased cake pan, smoothing out the top and ensuring there are no air pockets.

Bake for 40-45 minutes, or until a toothpick comes out clean and the top is golden brown.

Let the cake cool for 10-15 minutes then invert onto a wire rack to cool completely.