Preheat oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line with parchment paper.

In a bowl, whisk together flour, baking soda, baking powder, salt, cinnamon, and nutmeg.

In another large bowl, beat the oil and sugar together until combined. Add the eggs and vanilla extract, and mix until smooth.

Gradually add the dry ingredients into the wet mixture, stirring until just combined.

Gently fold in the diced apples and chopped walnuts (if using).

Pour the batter into the prepared cake pan and bake for 40–45 minutes, or until a toothpick inserted comes out clean.

Let the cake cool for 10 minutes in the pan, then transfer it to a wire rack to cool completely.

Drizzle caramel sauce over the cooled cake before serving. Enjoy!