Preheat your oven to 350°F and grease a 9-inch round cake pan.

In a large mixing bowl, cream the softened butter with both sugars for 2-3 minutes until pale and fluffy.

Add eggs one at a time, mixing well after each, then add the vanilla extract and mix.

In a second bowl, whisk together the flour, baking soda, cinnamon, and salt.

Gradually add the dry mixture to the wet mixture, stirring gently until just combined.

Fold in diced apples and walnuts if using.

Pour the batter into the prepared pan and smooth the top.

Bake for 40-45 minutes, checking around the 35-minute mark until a toothpick comes out clean.

Let the cake cool in the pan for 15 minutes before transferring to a wire rack.