Lightly grease a 9" round cake pan at least 2" deep; or a 9" springform pan.
In a large mixing bowl using a hand mixer, beat together the sugar, butter, and vanilla on medium high speed until smooth and creamy.
Add the eggs 1 at a time. Beat till thoroughly combined.
In another large mixing bowl, add the flour, baking powder, cinnamon, and salt. Whisk to combine.
Stir the flour mixture to the egg mixture alternately with the sour cream, using low speed on the mixer. The batter will be stiff.
Spoon the batter into the prepared pan, smoothing the top with a spatula to even out as much as possible.
For the apple filling
Plass the apple wedges in a mixing bowl and add the sugar Toss the apple wedges with the sugar and vanilla until apples are thoroughly coated.
Arrange the apples on top of the cake batter, pushing them into the batter gently so they're partially submerged.
Bake the cake for 65 minutes till it's golden brown on top and a toothpick or cake tester inserted into the center comes out clean.
Remove the cake from the oven, and turn it out onto a rack, apple-side up.
For the caramel topping
Place the caramels and heavy cream in a microwave-safe bowl, and heat until the cream is showing bubbles, and the caramel is soft. Stir the caramel and cream until smooth. (I did this in 3-30 second intervals)
Spoon the caramel over the cake, dripping it down into the crevices around the apples.
Scatter the walnuts on top. Sprinkle lightly with very coarse sea salt flakes if desired.