Melt the butter, sugar and cinnamon together in a large flat based saucepan for about 3 minutes until the sugar has melted. Pour in the apple cubes and coat with the cinnamon caramel. Gently cook for 5 minutes until the apple is just starting to caramelise.
Remove from the heat and spread the apples out on a tray in a single layer to allow to cool whilst you prepare the rest of the cake.
Pre-heat the oven to 180°C/ 160°C fan / gas mark 4 and line and grease an 8x4” round cake tin.
Cream the butter and sugar on a high speed in a food mixer for about 5 minutes until very light and fluffy.
Add the eggs one at a time and mix until completely incorporated. Then add the vanilla extract.
Whisk the sorghum flour, potato starch, ground almonds, baking powder and salt together in separate mixing bowl.
Take 2 tablespoons of the flour mix to sprinkle over the cooled apples. Toss to coat and set aside.
Add the flour mix into the rest of the ingredients, alternately with the milk, adding the flour in three additions and the milk in two (begin and end with the flour), scrape down the sides of the bowls as needed and mix until just combined.
Pour ⅓ of the cake batter into the tin. Followed by half of the apples. Then add another ⅓ of cake batter, followed by the rest of the apples. Cover the apple with the final ⅓ of cake batter and smooth the surface.
Bake for 50-55 minutes or until an inserted cocktail stick comes out clean.
Remove the cake from the oven and leave to settle for 5 minutes in its tin, then turn out onto a cooling rack and leave to cool completely before scattering with icing sugar.