Turn oven on and set to 170°C. Brush a bundt tin well with oil to grease and leave upside down over a plate or in the sink so excess oil can run off. In a large mixing bowl combine the dry ingredients flour, baking powder, bicarbonate of soda, salt & cinnamon. Mix to disperse ingredients.

In another bowl combine the wet ingredients vegetable oil, eggs, sugars, vanilla extract and milk. Whisk together. Then pour the wet ingredients into the dry ingredients and whisk until a runny wet batter is achieved.

Swap your whisk for a spatula or wooden spoon and stir in the diced apple. Pour the mixture into the prepared Bundt tin and bake for 50 - 60 minutes, until a skewer inserted into the centre comes out clean.

Allow the cake to cool for 15 minutes in the tin before turning out onto a wire rack to cool completely.

Meanwhile, whilst waiting for the cake to cool prepare the salted caramel by adding butter, golden syrup and sugars to a heavy based pan over a medium heat. Allow to melt together swirling the pan every now and again to help them. When it starts to bubble, give it a couple more minutes. Then turn off the heat and pour in the cream, be careful as you do as this can squirt a bit. When it has cooled enough so that you won't burn your mouth, start adding the salt a little at a time until to your taste. (I make it slightly less salty than i want, as i add more salt on top of the cake)

When the cake and sauce have cooled you can spoon the thick caramel over the cake letting it run down the sides. (there will be extra sauce for poring on as you eat to)
It is a good idea to set a plate under your wire rack to catch any caramel that runs off.
Sprinkle a little more of the sea salt flakes on top of the just before serving.