Preheat oven to 180°C. Grease and line the base of a 23 cm round spring-form cake tin with baking paper. Combine the raw sugar and cinnamon for the topping in a fine sieve or kitchen shaker and set aside.
Using an electric mixer beat the butter, sugar and vanilla until combined and smooth. Add the eggs, one at a time and beat until well combine. Add the flour, milk and apple and mix gently until just combined.
Scrape the mixture gently into the tin and spread evenly. Bake for 40-50 minutes or until an inserted skewer comes out clean.
Remove the cake from the oven and immediately scatter the top of the cake with the chopped butter and allow it to melt into the cake. Shake the sugar and cinnamon mix evenly over the top of the cake.
Allow cake to cool for 10-15 minutes in the tin and then carefully remove it from the tin and allow to cool on a wire rack.
This cake is best served on the same day as it is baked.