Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan. Optionally dust the bottom with flour.

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

In a large mixing bowl, use an electric mixer to cream the softened butter and sugar until pale and fluffy, about 3-4 minutes.

Add the eggs one at a time, ensuring each is fully incorporated before adding the next.

Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk until just combined.

Gently fold in the sliced apples and raisins or walnuts, if using.

Pour the batter into the prepared pan and smooth the top with a spatula.

Bake in the preheated oven for about 45-50 minutes or until a toothpick comes out clean.

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

Slice the cake and serve warm, optionally with a sprinkle of powdered sugar on top.