Begin by preheating the oven to 350 degrees F. Line two 9-inch round cake pans with parchment paper and spray with baking spray. Set aside.
In a medium bowl, whisk together the flour, cinnamon, baking soda, and salt. Set aside.
In a large bowl, add the eggs, sugar, oil, and vanilla. Use a hand mixer on medium speed to combine. Add the flour mixture and mix again until just combined. Fold in the chopped apples and pecans. The batter will be thick.
Divide the batter evenly between the two prepared baking pans. Bake for 50 minutes or until a toothpick inserted near the center comes out clean.
Allow the cake to cool in the pans on a wire rack.
In the meantime, prepare the frosting. Using a mixer, blend the cream cheese and butter. Slowly add the confectioners' sugar, one cup at a time. Add the kosher salt and cinnamon. Mix until the ingredients are well combined and the frosting is fluffy.
Transfer one cake to the serving plate and spread frosting on that layer. Top with the other cake round and add another layer of frosting on top of that. Smooth the top and sides of the cake with an offset spatula. Garnish with the apple slices and chopped pecans.
Serve immediately or store in the refrigerator until ready to serve. If refrigerating, allow the cake to come to room temperature before serving.
Notes
This cake can also be made in a 9 x 13-inch cake pan. Bake for 55 to 60 minutes. The frosting recipe makes a generous amount. Any excess can be stored in an airtight container in the refrigerator. Use the extra to dip apples, frost cinnamon rolls, or spread onto cookies. To prevent the sliced apple garnish from turning brown, toss the apple slices with a bit of lemon juice before putting them on the cake.