Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.

In a mixing bowl, combine flour, sugar, baking powder, baking soda, and salt.

Add softened butter, eggs, and vanilla extract to the dry ingredients and mix until well combined.

Fold in the chopped apples gently until evenly distributed.

In a separate bowl, mix brown sugar, flour, melted butter, and cinnamon until crumbly.

Pour the cake batter into the prepared pan and sprinkle the topping evenly over the batter.

Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean.

Allow to cool slightly before serving.