In the bottom of an 8-inch (20 cm) round cake pan, spread half a jar of vegan caramel sauce. Lay the apple slices on top of the caramel. Set it aside.
In a bowl, whisk together the flour, salt, baking soda, baking powder, and cinnamon.
In a separate bowl, mix together the oil, brown sugar, granulated sugar, non-dairy milk, flax egg, vanilla extract, and apple cider vinegar.
Add the dry ingredients to the wet ingredients and mix until combined. If you're using gluten-free flour, let the batter rest for about 20-30 minutes to let the flour hydrate.
While the cake batter is resting, preheat the oven to 350°F (180°C).
Pour the cake batter over the sliced apples, even out the top with a spatula, and bake it in the preheated oven for about 40-45 minutes, or until a toothpick inserted into the center comes out clean. Let the cake rest for at least 10 minutes before turning it out onto a plate or platter. Let it cool completely before slicing.