Preheat the oven to 350°F (175°C). Grease a 9x9-inch baking dish with butter or line with parchment paper.

Wash, peel, and chop the apples into small, even pieces. Set aside.

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

In a larger bowl, beat together the eggs, sugar, oil, and vanilla until smooth and creamy.

Gradually fold the dry ingredients into the wet mixture until just combined.

Gently fold in the chopped apples until evenly distributed.

Pour the batter into the prepared baking dish and smooth the surface. Bake for 40-45 minutes until golden brown.

Remove from the oven and let cool for 10 minutes before transferring to a wire rack.