Preheat the oven to 350 degrees and spray a 13x9x2" pan with cooking spray. Set aside.

To prepare the apples: Peel, core, and cut them into 1/2" to 1" chunks. Place in a small bowl and add the cinnamon and sugar. Toss to coat with your hands or a wooden spoon. Set aside.

To prepare the cake batter: In a medium-sized bowl, whisk together the flour, salt, baking powder, and baking soda and set aside.

Whisk together the oil, sugars, and vanilla in another medium-sized bowl. Add the eggs, yolks, and buttermilk and whisk again until incorporated. Add the dry ingredients to the wet, and, using a rubber spatula, gently fold the dry into the wet, until almost totally incorporated (a few little visible flour pockets is a good thing).

To assemble the cake: Add about half of the batter to the prepared pan and smooth it out with an offset spatula. Add the apples (optional: drain some of the liquid, if a lot has accumulated in the bottom of the apple bowl) and use a rubber spatula to spread them evenly over the first layer of batter. Add the rest of the batter and smooth the top of the cake (as best you can) with an offset spatula.

Transfer the cake to the oven and bake for 55 to 60 minutes, rotating the pan after 30 minutes, and checking the cake after about 45 minutes. The cake is done when a tester inserted into the cake (not an apple-chunk, ideally) comes out with a few moist, but not wet, crumbs.

Cool to room temperature before slicing the cake and serving with lightly sweetened whipped cream.

To store, do not cover the cake. Instead, simply cover any exposed sides with a strip of parchment paper. and don't cover it at all prior to serving. it will keep at room temp for up to 3 days.