1-Preheat oven to 180 C (350 F): Preheat oven to 180 C (350 F) standard / 160 C (320 F) fan-forced. Grease and line an 8-inch round cake pan with baking or parchment paper.
2-In a large mixing bowl, add flour,: In a large mixing bowl, add flour, baking powder, baking soda, salt and sugar. Add chopped apple and stir briefly to combine.
3-In a separate bowl, add eggs, vanilla,: In a separate bowl, add eggs, vanilla, oil and yoghurt. Whisk briefly just to break up the egg yolks.
4-Add wet ingredients to dry ingredients and: Add wet ingredients to dry ingredients and gently mix with a wooden spoon until combined – but be careful not to over mix. Spoon batter into prepared tin.
5-To make cinnamon topping, combine sugar, cinnamon: To make cinnamon topping, combine sugar, cinnamon and butter. Mix together until lumpy and wet. Sprinkle over cake batter.
6-Bake cake for approximately 30-35 minutes or: Bake cake for approximately 30-35 minutes or until a skewer inserted into the middle comes out clean. Transfer cake to a wire rack to cool completely.
7-To make the glaze, mix together sugar: To make the glaze, mix together sugar and 1 tablespoon of milk. Stir until smooth. If the glaze is too thick, add an extra tablespoon of milk. Drizzle glaze all over the cake.