Preheat the oven to 180°C (350°F) for standard or 160°C (320°F) for fan-forced.
Grease and line an 8-inch round cake pan with baking or parchment paper.
In a large mixing bowl, combine flour, baking powder, baking soda, salt, and sugar.
Add the chopped apples and briefly mix them in.
In another bowl, whisk together the eggs, vanilla, oil, and yogurt to break up the egg yolks.
Pour the wet ingredients into the dry mixture and gently stir with a wooden spoon until just combined.
Be careful not to over-mix.
Spoon the batter into the prepared pan.
For the cinnamon topping, mix cinnamon, sugar, and butter until lumpy and wet, then sprinkle over the batter.
Bake the cake for 30-35 minutes, or until a skewer inserted into the center comes out clean.
Let the cake cool on a wire rack.
For the glaze, combine sugar and 1 tablespoon of milk, stirring until smooth.
If it’s too thick, add an extra tablespoon of milk.
Drizzle the glaze over the cake once cooled.