Preheat your oven to 350°F (175°C) and grease your loaf pan.

In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon until evenly combined.

In another bowl, cream the softened butter, granulated sugar, and brown sugar together until light and fluffy.

Add the eggs, one at a time, beating well after each addition. Mix in the vanilla extract.

Gradually incorporate the dry ingredients into the butter mixture, stirring gently until just combined.

Fold in the diced apples and walnuts, if using.

Pour the batter into the prepared loaf pan, smoothing the top with a spatula.

Bake for 55-65 minutes, or until a toothpick inserted in the center comes out clean.

Allow the bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.