Preheat the oven to 180°C (350°F) for a standard oven, or 160°C (320°F) for fan-forced.

Grease and line an 8 or 9-inch round cake tin with baking or parchment paper.

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

Add the chopped apple and stir briefly to combine.

In a separate bowl, whisk together the eggs, vanilla extract, oil, and yogurt until the egg yolks are broken up.

Add the wet ingredients to the dry ingredients and gently mix with a wooden spoon until just combined—be careful not to overmix.

Spoon the batter into the prepared tin.

To make the cinnamon topping, combine the cinnamon, sugar, and melted butter in a small bowl.

Mix until it forms a lumpy, wet mixture.

Sprinkle the cinnamon topping evenly over the cake batter.

Bake the cake for 30-35 minutes, or until a skewer inserted into the center comes out clean.

Transfer the cake to a wire rack to cool completely.

For the sugar glaze, mix the powdered sugar with 1 tablespoon of milk and stir until smooth.

If the glaze is too thick, add an additional tablespoon of milk.

Drizzle the glaze over the cooled cake.