In a small bowl add in the flour, sugar and cinnamon. Mix.
Add in the butter and mix until combined. Place it in the fridge while preparing the batter.
Pre-heat the oven to 375 and line a 9x9 pan with parchment paper or grease pan and set aside.
In a medium bowl add in the flour, baking powder, and salt. Whisk and set aside.
Peel, core and chop the apples into small pieces and coat with a splash of lemon juice then set aside,
Cream the butter and sugar together.
Mix in the egg and then the vanilla.
Sift half the dry ingredients over the wet and then half the milk and mix until just combined. Sift over the other half of the dry ingredients then the rest of the milk. Mix until just combined.
Fold in the apples.
Add the batter to the pan and smooth out the top.
Sprinkle the topping evenly over the batter and press into the batter slightly.
Bake for 35-40 minutes or until a tooth pick comes out clean from the center.
Cool in the pan on a wire rack for 30-40 minutes before slicing and serving.
Serve with some ice cream if you'd like or custard